I wish I could tip more than I do, but with the training costs I keep a very tight budget, I have no other choice really..... I mean, the bill comes out to about 20 anyway if you are in a large group of college kids, even if you're meal was just a burger and soda.
When I was working in my boring cubicle job, I did have the money and tipped well, it was sort of my way of saying "thank you." Now, I just leave what I can on top of what the bill is, and scamper out of there hoping not to be shot at!