Getting so close to leaving

You won't need euros for the bathroom in the airport. Waiting until you get to your destination and withdraw a small amount from a bank-affiliated ATM, but make sure your bank won't charge you an international transaction fee.
I haven't been to St. Tropez, so I can't answer about which beach club. SO not my scene.

The only euros I have on landing is whatever I brought home on my last trip - which isn't much. As for bathrooms - you would need coins, which you can't get outside of Europe anyway (unless you have a friend who brought some home). You might be surprised to know that even some bathrooms can be paid with your contactless credit card or Apple/Google Pay. Get a small amount of cash from any bank owned ATM after arrival. Any transaction fees by a bank is small potatoes compared to the cost of your vacation. Then buy something small at a shop to break your smallest bill, and get the change in coins.

Here's our host's advice about money, including your question. Can't help you with the beach club issue.

In the past 5 years I've done about 15 round trips to France and haven't taken out any cash whatsoever.
Now I love here and I think I have collected 30€ from friends paying me their part when I pay with card. France is very much a card society now.

Speaking to your Disneyland Paris time, you won't need cash there either you can pay with card or digital wallet and there is no fee for the restrooms. I recommend using the park's mobile app to keep track of the ride wait times (they are pretty accurate) as the most popular rides in the two parks do not have skip-the-line options. If you're staying at a Disney hotel, you get in an hour before general admission. Take snacks with you, the food choices were really quite awful.

As someone who goes on vacation near Toulon 1-2x/year, I really would not bother with St Tropez in August (traffic, crowds, prices), when you have better beaches close to Toulon. For example, you can go to l'Almanarre beach near Hyères and book a table at Gaetano (nice, large pizzas - best to share). Porquerolles is also a fun day trip. Or, for something easy and close by, take the ferry from Toulon to Les Sablettes; the beach there is fairly nice with a wide selection of usually decent restaurants, some of which with lounge chairs on the beach (e.g. Le Carré Plage).

If you must go to St Tropez, Pampelonne or Tahiti beaches (it's the same long beach) is where you want to go for beach time, but restaurants / beach clubs are absurdly overpriced in my recollection.

A word of caution: I do find that restaurant review scores are a bit inflated in the Toulon area compared to other parts of France. A 4.5* Google score isn't necessarily particularly good IMO, so do take a bit of time reading reviews.

Last but not least, regarding cash: you do come across the odd cash-only establishment around Toulon (and probably Nice as well), so you'll want to withdraw some - basically enough to pay for a meal for the family should the need arise. But no need to take any with you from the USA.

Good heavens. Several hundreds of euros?

Tap to pay is ubiquitous in France. Unless you're credit-phobic (and that's a valid concern), you're unlikely to need more than a couple of €20s.

When we left our gite in the Dordogne after ten days, I opted to pay the caretakers to clean the place. It was 100 euros and they wanted cash, which I happily provided. There had been seven of us, and it was nice to let things be. (I also opt to not do the cleaning in the states, with VRBO, etc., but that can be done through our VRBO booking by CC.)
We always take about 100 euro with us. At local markets the vendors seem to prefer cash for smaller purchases, and we always drop something in the donation boxes at churches, especially the poor boxes. Any leftover cash will be used on the next trip, or handed to our offspring for their trips.

When cleaning out my parents' house last month, I found my dad's snack-size Ziploc baggie with his euros in it and his note detailing the amounts. His (and my mom's) last trip to Europe was to Scotland and France to celebrate their 50th wedding anniversary a couple of months late (grandkids' summer schedules) with me and my brother, our spouses, and my brother's kids. There was 95 euros and some change in the baggie.

Next week my niece is coming to stay with me a few days before heading to Rome,.where she is taking a four-wheel course. I know her grandpa would want her to have that for fun money, so I have set it aside to give her.

It really depends on where you travel. If you limit yourself to cities, then little if any cash will be needed. But when going to rural France, many vendors and stores appreciate being paid in cash. The little mom & pop B&B I stay at in Normandy asks to be paid in cash, and I am happy to oblige. Always have coins however. In addition to small tips and many toilets, grocery stores often have you insert a coin to release a shopping cart. You get said coin back when you return the cart.

Tap to pay is ubiquitous in France.

According to data from the latest study by the Bank of France, 43% of payments in France are still made in cash, 48% by credit card, 4% via mobile phone, and 5% by check.

Also according to Bank of France data, 60% of French people consider it important (or very important) to have the ability to pay in cash. Transaction anonymity, ease of use, and the perception that cash helps people better manage their daily budgets are all arguments put forward to emphasize the importance of paper currency.

In rural areas or small towns, I can see this firsthand every day, many people still pay in cash. For my part, barring exceptions or small amounts under 10€, I use my credit card but I always carry at least 20€ with me just in case (along with plenty of coins for exact change). My baker, if she's having a bad day, will refuse to let you pay for a 1.20€ baguette with a credit card and she might even throw you out of her bakery, yelling at you not to come back! :-)

It's her right; the only form of payment a merchant is legally obligated to accept is cash, provided you don't pay with more than 50 coins.

Those are interesting stats, JoLui. Thanks for sharing the true data. Anecdotally, I have rarely had occasion to use cash anymore in France as tap to pay is everywhere even in the small villages around us. However I do run in to exceptions such as the weekly markets (WiFi isn't always working in the markets) or toilets. So cash is preferred. Because of these two things I always keep about 20 euros on hand (some in change.) Rarely do I ever carry hundreds of dollars unless I know that I will need to pay cash for something specific such as a private tour guide, purchasing something at a brocante, or paying the gardener. If I do need extra cash, I go to a bank ATM to get what I need. But stepping off the plane in France, I usually only have 20 euros.

Evidently a lot of people like cash much more than I do. Apologies to those who were offended by my remarks, but I still do believe that there's no real need to load up on euros when visiting France, even if you're visiting small towns and the countryside. Preferences are an entirely different matter, obviously.

While you do need cash in France, especially the south east and the countryside, ATMs are easy to find and usually cheaper than getting euros abroad, so do take maybe 100€ with you if it makes you comfortable, but for larger amounts I would rely on ATMs as money exchange office commissions do tend to add up.

I have been to France twice in the past year. I keep taking the same 40 euros I brought back home to the US from a trip a couple of years ago. When purchasing a drink or ice cream cone or a small trinket/souvenir many of the shops have signs "card only". They do not want to keep cash/euros on hand and be expected to make change. Using a card is easier and faster for the merchants. They have priced their goods for sale to include the fees they must pay to the card services.
Last month in Nice my transfers wanted credit card for payment. Visa or Master Card - not Discover and sometimes not AMEX
I agree that outside of the cities, your experience may be different.

I usually get some Euros from my local bank, because I can specify small denominations in advance. I can't do that at an ATM. So, in your situation, I might get 100 Euros in smaller bills and split it between my husband and I. (Since it's your first trip, of course you can't be expected to have any leftover Euros from previous trips.) It's probably not strictly necessary, but it's nice to have for tips, incidentals, street vendors, etc. Do note, though, that tipping is less common in Europe than in the US, and the tip amounts don't tend to be as high. (Either round up, if paying cash, or tip 10%, depending on the situation). Do watch for "service compris," on your meal bills, too. That means the tip is already added to the bill. If you do wish to tip, their machines aren't usually set up to add it to a credit card payment, so you'd leave a small cash tip, if it wasn't included in the bill, or if it was, but you'd like to add a little more for particularly good service. (Not mandatory, and not necessarily expected, but probably more expected in heavily touristed areas.)

Enjoy your trip!