Outside of a bottle of water, if I forget mine at home, string cheese, the elusive Zagnut, etc. There's not much I want or need so it gets donated.
This way, I'm not stuck with something I don't want and kids in my community, who may see little to no food outside of school, have a little something to eat.
When the reimbursement is a buck, I go for bricks of ramen, granola bars, crackers, etc. For $2, it's larger packages of noodles, fruit cups, or Chef Boyardee. I fill a medium sized box for my local elementary school's backpack program. The amount over the reimbursement is still cheaper than whatever the item costs at Walmart.
Because there's a plethora of grocery store shops nearby, I'm lucky enough to almost always buy my groceries on mystery shop. Most of the time, I can get a 6-pack of ramen, boxes of raisins, tuna/cracker kits for under $2 and apple sauce or pull top cans of soup for under $3.