The short version: The homeless can use their food stamps any place any other recipient can use food stamps, anda few other places as well:

At homeless shelters or soup kitchens if they so choose:

Homeless people can pay for meals with food stamps at some soup kitchens and homeless shelters authorized by USDA. [7 C.F.R. § 274.10(g); MPP § 63-604.5.]  No one can make a homeless individual give food stamps to the soup kitchen or other emergency meal provider. [7 C.F.R. § 278.2(b).]  A soup kitchen or emergency meal provider cannot make people who get food stamps pay for meals if other people get those meals free. [7 C.F.R. § 278.2(b).]  Soup kitchens and other emergency meal providers cannot make people pay with food stamps for food that they got for free or for any of their costs cooking the food or running their place. [7 C.F.R. § 278.2(b).]  They can only request that homeless people voluntarily use their food stamps to pay for meals, and cannot ask them to pay more than the average cost of meals at the shelter. [Id.]

At restaurants and grocery stores in some counties:

Homeless people may use their food stamps at certain restaurants and grocery stores to buy prepared meals. County welfare departments in California contract with these stores and restaurants to provide meals for the homeless (and elderly and disabled). [7 C.F.R. §§ 271.2 (definition of "eligible foods"#9) , 272.9, 278.1(i); MPP § 63-102 (e)(2)(H).]  Participants are given a specially-marked ID card to use with their EBT card at these locations. [7 C.F.R. § 274.10(a) (4) (iii); MPP §63-102 (e)(2)(H)3a.]   In California, the county must submit a written proposal to the California Department of Social Services before the program begins. [See MPP § 63-102 (e)(2)(H)3-4 and ACIN I-32-12.]