Just get something from Costco, they have huge bulk sized containers of snacks. Anything from candy to granola bars to pretzels to cheese puffs etc.
You don't have to give them a "meal."
Just a snack. At most.
Or get boxes of Capri Sun. These are often on sale.
I would not get, perishable type foods. You would have to keep it refrigerated.
Just don't get anything with nuts... as schools often have a "no nuts" policy.
Also, if the kids don't show up, then how does the school... track them and their progress? Are their parents told that their kid did not show up?