Ziploc bags? Have heard they are expensive there.

OP here. Thanks so much for everyone's comments and suggestions. Here is what I decided to take to everyone:

7 year old daughter of best friend: Felicity American
Girl doll (the American Revolution doll) and Big League Chew

10 year old boy and 13 year old boy: DC United Tees and a Chicago Bears football and Big League Chew

Parents: Peanut butter (creamy AND crunchy), box of salt water taffy and a Washington, DC travel guide (to encourage them to come visit me).

Old Teachers: Peanut Butter, Washington DC Travel Guide, Back issues of Washingtonian magazines (they were English teachers and I thought these would amuse them), Salt Water Taffy, Peet's coffee (DH went to Berkeley and I think my old ultra leftist teachers would love this) and a couple of little things for their grandson.

I am taking extra boxes of Salt Water Taffy for other old friends that I may see as well as extra Big League Chew packets for their kids.

I am not going to Eurpoe or sending gifts any time soon. . .just wanted to say I have enjoyed reading this thread and everyone's comments. So interesting. . .I never thought about the fact that I didn't see PB when I lived in Europe.

Marmite on the other hand. . .

My sister lives in Germany, and when returning there after a summer vacation here in the US, as gifts, she brought back lots of spice packets and condiments that weren't available/easy to find in Europe. For example: Ranch salad dressing packets, chocolate chip cookie mixes, Old Bay seasoning, Frank's hot sauce (for buffalo wings). Her kids also love oreos, something they can't get in Germany. I also second the PP's who mentioned Reeses peanut butter cups and peanut butter. When I lived in Italy during college, it was difficult to find peanut butter and when we did find it, it was pretty expensive.

I'm the PP - we also gifted an "American" cook book because one student was studying hospitality and included measuring spoons, cups, and a liquid one cup measure to make it easier. She LOVED it. Her family runs a cafe in a seasonal (ski) resort and she has written about some of the "hits" from the recipe book.

We have hosted exchange students and Peanut Butter is a huge hit - you can buy in Marks Spencer grocery area in Europe, but natives don't shop there . Also any kind of chips - our most recent student used a reusable Trader Joes bag to take back Kirkland Potato Chips and Sun Chips.

We have found US football items (shirts especially) were popular too - as an oddity, not because they follow it. Our Austrian exchange student from the fall TRIED to figure it out, but it is like me following Australian Rules football - so not working!

I haven't had that problem with German customs.

I am in the same boat - I love all of these ideas but have heard that German customs is very strict.... will they take all the food items (ie bisquick, brownie mix...) away in customs?

We have family and friends in Germany - one of the other things the moms like us to bring for their kids events are the 'sprinkles' we can get for on top of cupcakes - Christmas and other holiday ones are a big hit - we added pancakes and syrup to our traditional list of choc. chips, jelly belly jelly beans, and Reeses PB cups.
We have also sent over some of the summer toys we have here - Slip N Slide was a big hit for awhile.

My nephew is here right now and he has a list with him from all his friends - some sport jerseys and special jeans are on the list - also a certain kind of sneaker ( chico's ?) - he is 14 y.o.

If they live in Europe the boys may be pretty attached to particular soccer teams already. If you want to bring sports jerseys, I'd go with the quintessential sports of baseball or American football. I completely agree with the maple syrup and brownie mix recommendations. What about Jiffy Pop? It looks so crazy/fun when you cook it. I've brought Pop Tarts and Oreos with me as well when I've gone over there. Don't know if they have Pop Rocks candy in Europe, but what kid doesn't like that?

My teenage European nieces/nephews LOVE Abercrombie & Fitch or Hollister clothing, which they tell me is very trendy in their school. I think there are some A & F stores in Europe, but not where they live. T-shirts and hoodies are favorites - look for them on sale. Hollister is the same company with pretty much the same stuff for much less $$.

I'm going home in a few weeks and all your ideas are great, my list includes Peanut Butter (Teddy Bear brand), Maple Syrup, Pancake mix, (I'll add Toll House cookie dough), Red Sox hats (for the kids), and of course microwave pop corn (not available in Europe, at least in Belgium!) Thanks for all your suggestions, it's always hard to find what to bring, I always know what I want to bring back from Belgium, but never know what to bring.

Converse High tops are very popular in Europe with the kids -- and more expensive than the US.

How old are the kids?
How about halloween outfits? They are not sold in such large quantities or variety. I sent a princess dress from Target of all places to my neice and apparently she became speachless when she saw it.

Kraft mac-n-cheese.