You can't use food stamps at McDonald's. But you can use food stamps for food, and divert money you would have spent for food into going to McDonald's, I guess... is that what you meant?
You can, however, buy things like cola and salty, high-fat Cheezy-Poufs, various Starbucks grocery items, etc. on food stamps, in most places.
What I always thought was strange, is that you cannot buy anything freshly prepared at a grocery store - no sliced meats or fresh seafood, no deli-prepared dishes, nothing like that - at least, until they've been shrink-wrapped and price-stickered for later sale. THEN you can buy them.