Hello.

One thing which is worth trying is going to supermarkets (Tescos, Sainsburys, Iceland, Lidl) at the end of the day because they reduce prices of fresh things that they won't be able to sell the following day. There is usually a special section of this reduced food so if you can't find it then ask someone who works there.
Another possibility is going to a Pret A Manger at the end of the day because they throw away their sandwiches so will sometime give them to you if you ask. I once got a whole bag of sandwiches!

I hope this helps.