What does "Donating for provisions" do?
Solution 1:
I believe donating food raises moral and people are more likely to donate to the camp. You don't have to donate food and you're probably better off selling it to a butcher in a town.
Solution 2:
Donating for provisions adds to the supply of the camp. This is unlocked when you can start upgrading the camp otherwise it's fairly useless to do so. If you don't donate for provisions that resource has to be refilled at the ledger and be paid the resupply fee.