As I have mentioned several times, my grandmother is on food stamps (and has been for years). I help her with her shoppping each week, so I'm fairly familiar with the program. It is true that you are not allowed to buy alcohol, tobacoco, hot food, and non edible household supplies (toothpaste, paper towels.....) They can be used to buy junk foood (chips, snack cakes, soda....) however. While you may need to reverify eligibility to maintain enrollment, there is no maximum enrollment period.
But in practice there is, because single people are only eligible for 3 months in any something-year period (I forget the exact number of years, maybe its 3 or 10). Obviously, old people such as your grand mother, or people who can prove some other sort of incapacitation can get them longer, but 'able bodied' adults cannot get them regardless of economically imposed unemployment, for more than the 3 months.