I can only talk for my local one. They are mainly a community shop so obviously they buy and sell food.
I have a monitor on my TV that documents the adverts I watch, in return I can choose from various vouchers, the vouchers are worth about £10 a month.
I don't need them at the moment so I asked if they were useful to the community shop. They asked for Argos vouchers which I thought was because sometimes they have families moving in to the area with nothing and you can get lots of household items there.
What they do, which they actually asked if I minded, is raffle them, that turns a voucher in to a pallet of food.
Mine does give out food that is out of date but not as part of the food bank or shop, they are just put on a table for people to take.
The foodbank is a bit different because of the shop, so they can give out fresh meat and veg. They also have a policy of giving out 'a nutritious meal' so for a family, as well as the tins / packets they might get a (frozen) chicken, potatoes and veg with maybe some gravy granules or stuffing.
I'm on a large council estate so some of the people who need help might have left a refuge or be an asylum seeker. As someone said above, people don't always have a fridge or freezer, when you move in to a council property you get the property, no flooring, curtains, cooker, fridge.
So it is a good idea they also run family cooking where families come after school and cook a meal together that they can take home.
They also run cooking classes because not everyone knows how to cook and even if you do if you have just arrived from Libya or Somalia you might not know what to do with a tin of baked beans.