Based on things that I've missed in the past when I've been gone for a while. Heavily influenced by the West Coast
1. The Beer
Specifically the delightful variety available. I will miss you, obscenely hoppy but thoroughly delicious IPA's. No one makes them quite like you do, Pacific Northwest microbreweries!
Actually, a lot of Asian or Asian-influenced food. What I've had back home and elsewhere is usually sorely lacking or overpriced.
3. C/D-list Celebrity Culture
This headline would be greeted with puzzlement in most of Europe, and not just because we wouldn't know who that is.
4. Convenient Store Hours
You need tampons and it's 7PM? Tough cookies.
5. American Optimism
Yes, I'm a raging European cynic/pessimist, and optimism is a strange thing to me, but damn if I don't admire it.
I'm sure there's more... anyone else who's traveled or lived abroad care to chime in? I've been trying to get as many "last time" things in before I leave and based on past experiences, I know there's quite a few things I won't think of until it's too late!