good thing youre not famous, you might go into the shitty tipper database
http://www.bitterwaitress.com/std/
I always overtip.
I worked as a waiter for a few years a while back and some customers can be true assholes with their stupid fucking demands.
I give
a buck a drink
a buck a bag
$5-10 for groceries
18-20% at restaurants and for really good service it's always ok to give more