Yeah, I usually don't get coffee either, and while I feel fine tipping if I get a strawberries and cream frappucino or whatever, I do always feel vaguely stupid tipping for having them get me a cookie and a bottle of water. That's part of why I did this, so I can get a feel for how tipping usually works with other people.

And I don't use cabs that often either, but I do on rare occasions (like the other day it was storming cats and dogs when a friend and I got out of a Shakespeare play, and since we'd walked I called us a cab), so I figure it's worth figuring out.