Thankfully I have never been on benefits or needed to use a food bank. However I think it must be a pretty degrading experience to have to go to a food bank and be dependent on whatever the public have donated. A civilised country should help vunerable people through taxation rather than charity.
Getting the general public to donate food they have bought at Tescos is not a cost efficent way to stock a food bank. It is hard for the public to know what the food bank needs. They might end up with loads of tins of soup when the reciepents want cornflakes. The reciepents might not like the food on offer. If the food banks bought the food direct then it would be possible to have some fresh food. (ie. fruit and veg)
I feel that people who are desperate enough to need a food bank should be helped through loans/ grants so that they can buy what they need. I can see a place for food parcels for those with severe learning difficulties, housebound or drug addiction. However if you are going to give a food parcel then it needs to contain everything they need. If the food bank had grant they could buy what they need in bulk.