Back to the poster's original point, if you go to Whole Foods, and order from their deli windows, and then pay for the food and take it to the seating area, you don't have to pay a tip (I've never seen a place to do so, even). And the food is pretty good.

Another idea: farmers' markets. I've never seen a place to tip at one of those.

Renting an apartment would allow you more opportunities to buy groceries, thus avoiding possible tip-inducing situations.