I'd note, though, many Europeans hate peanut butter. Bizarre, I know.
As per the suggestion re: choco chips and brownie mixes, I might suggest bringing pancake mix also. I've just gotten back from living in London for two years, and never saw a pancake there. Which I find odd, as folks there definitely have sweet teeth (if that's the right plural

). I'd suggest bringing that.
The other thing they don't have, at least in the UK, is corn bread. This might be an acquired taste also, but I suspect folks there would like it. You could bring some of those Jiffy corn bread mixes, and I bet they'd be a hit.
If you are bringing baseball hats, I would suggest either Yankees or Red Sox hats. I doubt any other teams would be recognizable over there.