I have three bags of bags. I don't need three bags of bags! Realistically, I need two bags. Maybe a spare. I used to work in a supermarket and they have mostly been accumulated from customers leaving other store's bags behind 
They are the 50p-£1 type, heavy duty ones - would food banks take them? Charity shops? I suggested giving them to customers who had forgotten theirs, but that wasn't allowed, because that would stop them buying new ones!