Most food stamp recipients I know and see do have jobs and disproportionately single mothers, most often with only one kid. They do not appear to be breeding as well as the general population thus contributing to the shortfall of future tax payers more than just by not making enough to pay "their share".
Sweet soda pop, like milk is a hydrated carbohydrate source, but the soda pop keeps and transports better; an important consideration when eating on the run and lacking a lot refrigerator space. The bagged snacks and candy are also more durable, denser and less expensive energy sources, especially when considering the cost per calorie relative to healthier fruits and vegetables.
It would also be interesting to know how the food stamp recipient sub-population compares to the general population in regards to lactose tolerance.