In the wallet? Yes, as given you're in the US, you can't use them except to post (which is a bad idea). I keep my Euros (and USD, not that I'll be using them anytime soon) on a shelf, and try to remember to grab them when I travel.

I've forgotten them once, which was silly, but it beats carrying them constantly.

Alternately, you're as skint as me, and have a few Euros and bugger all USD as well, in which case, well, cash them in?

I love the idea of the Euro, it'll make travel so much easier. Then, I love the idea of a global computer based currency, I lived out of ATMs in the States, Vince found it amusing.