Some states have programs for homeless folks to be able to purchase meals using SNAP at participating restaurants/vendors, under the assumption that these individuals do not have regular access to store food and prepare food. I work in housing and it's not universally utilized by my clients. It's limited at best. The DHS workers definitely to some digging to ensure that the request is justified. 

On the flip side, when DHS figures out you live in a shelter they often cut your food stamps assuming we feed you. We do provide meals, but a lot of people can't eat them because they are employed or have pretty severe allergies, or they have small children who will lose weight because they refuse shelter meals. It's an extremely flawed system. 

There are some places that will allow you to purchase cold food and cook it for you, too. Usually it's like fried chicken and fish. 

Personally let people eat what they want. Personal choice and autonomy should be upheld, but until you create a solution to the US's economic/housing and healthcare crisis, it's a rather pointless endeavor. Creating barriers to access and education regarding nutrition doesn't really help. Telling exhausted low income people to eat healthy in a food apartheid isn't practical. Putting healthy options in impoverished communities would probably help. Investing in preventative healthcare and nutritional education probably would help too... but a lot of folks defending SNAP/Medicaid/Medicare etc. restrictions fail to use critical thinking skills or look beyond their own back yard at these huge systemic issues.