What do I need to book in advance?

I can give you some Hints on Paris/Mont St Michel:
Pre-book the train from Paris-Mont St Michel, it should be a train/bus combo ticket. We used Captain Train and had to print out our tickets at the train station at a kiosk (no problem). The price increased substantially as the days got closer to our trip, so book early! We purchased the Paris Museum Pass and thought it was a great value, no need to pre-book anything just be very careful to closely follow the instructions.

You can pre-book a Seine River cruise for a small discount. We did just the river cruise, which was a must do and next time I think we will do the Dinner Cruise.

Thank you so much for the input. I should have added that we will be picking up a car for our travels after our stay in Paris.

Are there many Seine River cruise companies to choose from? Are they all about the same?

We took the Bateaux Vedettes du Pont Neuf cruise and were happy with it. You can buy tickets online which are good for 1 year and can save about 3 euro. You just print them out and show them when you get on the boat.

We also did the cruise with Bateaux Vedettes du Pont Neuf , pre-purchased and printed at home.

Nice thing about a Seine cruise -- you can drop it in your schedule when the weather looks best. I like the Pont Neuf cruise, but that's partly because we stayed nearby. Nice park to eat a pre-purchased snack while you wait for the next boat (unless you manage to arrive just in time for a cruise.)

One question about what was told to RGS....the pre booked Seine tickets can be used at any time? You don't have to give them a day or time when you purchase them? Linda

My recollection is that there are two prices, for day and evening cruises, but nothing else needed to be specified. I bought tickets online the day before, got a confirmation number and just showed up at the dock.

They run so many cruises that they don't require a specific time.

For museums, you don't need to book museums per se in advance, but you will want to think about whether you want to purchase the Paris Museum Pass for a certain number of days. The pass can be purchased either at the airport upon arrival, or at one of the smaller museums the first day you want to use it. Think about the places you want to see, see what proportion of them are covered by the pass, and think about how much you want to be "pressured" to use your pass -- i.e. the two-day pass is cheaper, but you will likely feel compelled to run around museum-ing those two days to get all the value for it, which can actually be detrimental to your stamina and staying power!! Also, don't think of the museum pass ONLY in terms of money saved for the number of museums you want to see -- a key component is the TIME it saves you from waiting in the longer lines to buy tickets at most museums.

You'll find lots of posts on the Forum about the Paris Museum Pass and whether it's "worth it" or not - the general consensus is yes, but of course every single traveler has varying aims for their time in Paris!

http://en.parismuseumpass.com/

So in other words - it's not something you need to reserve in advance, but it is something to think about in advance.

Thank you Laura B and Kim!

Kim, do plan on getting the museum pass for 2 days. I could use a 3 day but its not available and 4 day is too many. No sense paying for an extra day you can't use. Also, I will be in Paris on the first Sunday of the month when a lot of these museums are free. But really don't want to rely on that as I can imagine how much more crowded they will be on a free day. But can fall back on it, if there is a desired museum that I didn't get in during my 2 days. Besides, I'm one of those people that feel the cost is worth it just for the time saved not having to stand in line. Also, since only have a limited amt of time in Paris, don't plan on filling it up with a lot of museums.

Sorry RGS, didn't mean to jump in. Thank you for your understanding.

When you say MSM area do you mean you are not staying on the island? I hope you will try to spend at least one night on the island... It was such a special experience to wander around after all the day trippers left. It has to be one of the highlights of many nights spent in Europe. You just park in the specified area and take a shuttle over... It was a little confusing, but somehow I figured it out.