How much did you spend?

Depending on what kind of entertainment and food you're planning, I would think a single person could get by on $75 to $100 per day.

Celeste is about right. $40-$50 per day for food & beverage (less if you don't drink alcohol or soda), and you'll need admissions to sites, local bus or metro fare.
On occasion you'll need laundry money (laundromats are expensive) and maybe internet access fees in some places. Check with your hotels on what they have and wht they charge. Some have free WIFI in the lobby, for example, but charge if you connect in your room.

Since I'm a natural tightwad, whenever I hear this question my mind rephrases it to; "how little can I spend..." The answer to that question is around $20/day. Assuming your accommodation supplies breakfast, you can easily get by eating for $20/day as long as you drink tap water. Even less if you eat from grocery stores. Any answer beyond that assumes we know what you plan to do while there, so it's a little absurd to guess. You can do a lot of strolling, photography, many cathedrals and churches and people watching (and the occasional free museum) for free. Most museums and iconic sights have a fee and those fees can add up fast. Drink alcohol, eat fine food or go shopping and all bets are off. Have fun!! You can get by on very little if you need to.

2 week budget Hotel: covered Transport: covered Sitting on Spanish Steps: $0.00 Replacing cell phone left on Spanish Steps: $400 Data Plan, texting: $15,000 Data Plan, uploading video to Face Book: $52,000 Data Plan, on line mobile gaming Prince of Persia $35,000 Museum(s): $12.47 Beer and pizza: priceless

I agree with Randy. Of course, you should plan for the what-ifs of vacationing and also bring extra for who-knows-what-might-happen, but in all honesty, you do not have to feel obligated to spend $50-$100 per day. If you have that saved, then fine - you may be able to enjoy some added bonuses that the rest of us poor folks can't :-)
But if you are on a budget, and saving that much is not reasonable, then don't feel you cannot have a good time. Do you spend $100/day at home on average? Then why feel obligated to spend that just because you are overseas? You can very easily find low-cost, high-quality restaurants in off the beaten path neighborhoods instead of sticking to touristy-areas. You can go to open air markets and bargain for gifts and souvenirs instead of shopping in high-end stores. You can live like a local (ride the bus or subway, walk) instead of like a tourist. And take advantage of the free stuff like people-watching, aimlessly walking in an atmospheric neighborhood, etc... I'm not knocking anyone that suggests you spend more. Like I said, if they can, or if you can, hey that's fine. And it's not about being "cheap" to spend less. But I work part-time and I have strong feelings about people who are on a budget still being able to travel AND enjoy every minute of it just as much as someone who can afford more. Hope that helps!

Just so you know, don't bring a lot of cash. You might want to buy some euros in the U.S. so that you'll have some local currency when you arrive, but get the rest of your cash from ATMs. Tell your bank when you'll be there and in which countries so that they don't flag your account.

Twenty-five bucks might be tight if you have a lot of entrance fees or suck a lot of beer. Fifty is a big over-kill. I have no idea what entertainment means.

Randy is on the money (no pun intended, there). My first trip to Italy was 16 days, with my wife, and we spent about $4000, which is about $125/person. This total included Train transportation, but not airfare. With that being said, we ate out every dinner, and quite a few lunches, too. We like wine, so that was consumed quite a bit. We saw everything that we wanted to see, but we walked everywhere, no public transport (except for trains, which are paid for you). We stayed in clean places, but not classy at all. If you're choosy in what you see (lots of free stuff to do) and picnic a bunch, you can spend way less than that.

I should clarify that the dollar-euro conversion was more favorable back then, but all that I've said will still hold true. We were in Italy again this May (with my daughter this time) and I still feel that you can exist for far less than $100/day. One other note: you mention that train travel is paid for. Is this a rail pass? If so, bear in mind that there are times when you will be required to pay a reservation fee with your pass. There may also be times when trains are "full" to pass members, when seats may be available to ticket-buying travellers.
Have fun!

We're with Denise. Our hotel breakfast also lasts us till afternoon and with either market picnic lunch or street food, crepes in Paris, pizza in Italy, we spend little money. We also sometimes have a picnic in our hotel room for dinner, especially if we're tired from walking around all day. In France we found traiteur or deli where we bought cooked vegetables and meats, and wine. With a trip to the bakery for bread and desert we were able to have a delicious dinner. We did also eat dinner out. Since you're only 19 yrs old you probably wouldn't be interested in expensive restaurants anyway. By buying food from markets or delis you can eat for a lot less with the benefit that you have a better idea how the Europeans eat.

What you have to watch with the breakfast with the room business is the differential (if you can get it) between that and a room without breakfast. Except for the UK and RoI, I've never found that I couldn't do better with just the room and snagging some bread and cheese along the way.

I usually budget about 75 Euro/day for food, drinks, entrance fees, metro, etc (unless you are planning on doing some very fancy dining). This is about $100/day. As a (slightly older) young lady myself, I would caution the following, specifically if you're a shopper (and definitely if you're a shopper AND headed to Florence): bring extra money (or a credit card) and an extra suitcase. a large duffel bag is good because you can fold it down in your other luggage on the way there and just use it as you accumulate new stuff. I had to buy an additional suitcase in Florence when I went because the leather jackets, purses, shoes, and scarves would NOT fit in the carry-on sized bag that I brought over there. :)
Get a few (200 at most) Euro before you leave the States in case of emergency, otherwise use ATMs to get cash while there. Make sure you call the number on the back of your ATM card and any credit card you plan to use over there to tell them the dates of your trip so that they don't disable your card for fear of fraudulent activity. If you have multiple credit cards, ask when you call if they charge a foreign transaction fee (usually 1% of the purchase) - I found before I went to Europe last month that one of my cards doesn't charge one, so that is the card I used. Have fun!

As previous posters noted, if you have your breakfast included with your hotel, that will start your day. For us, breakfast will take us to about 2 p.m. We then have a sandwich that we make from fresh rolls, salami and cheese that we purchase from the market (Coop). At the deli, they will slice the meat and cheese for you. We'll bring a soft-sided, foldable cooler from home to keep our food chilled. Sometimes I'll bring a gell ice pack and put it in my checked luggage. Bringing ziploc bags also helps (haven't found these in Europe yet). So, for lunch, it's about 10-12 euros for both of us. However, we'll often have left overs for another time. For dinner, sometimes we do a picnic and sometimes we go out. With wine, beer and food we spend, for two people, about 20-25 euros. Have fun on your trip!

For two weeks I'd consider doing laundry in the hotel sink. Also, if your hotels include breakfast, that will help your budget. When choosing a restaurant, the heavier the silverware and the longer the stems on the wine glasses, the more expensive it tends to be. Museums and other sites can really add up fast (especially if you go through the gift shop), but you probably don't want to give up these experiences just to save a few dollars. Best trip advice I ever got: take half as many clothes and twice as much money as you think you'll need.