I've seen my share of those , load up a cart and when their bill was more than the amount of food stamps they had they would put everything back but the junk food. Some would offer $5-10 in food stamps in exchange for $4 to us pushing carts in from the lot in case so they could buy cigarettes (and get mad at me when I wouldn't take them on their offer).
I got paid weekly and allocated $20 to groceries our of my $100 per week take home pay, I got lunch at school and at work sat and Sunday when I worked 8 hours so that had to do breakfast and dinner for a week. I'd get the $0.19 loaf of bread, the $0.99 eggs, $0.99 gallon of OJ, $0.79 imitation pop tarts, cans of soup or such that was on sale. It was almost a game to see how far I could stretch that budget.