I second Legs Akimbo's point about frozen berries. At Tesco, one can purchase a very large size box of frozen berries for 2 pounds. The quality is very good. I make pulses/shakes out of them, or just defrost and eat with some light whipped cream. Yum.
Otherwise, the arab market near to us also has great fresh fruit deals. They sell 6 large lemons for 1 pound, or 6 limes for 1 pound. We make a lot of lemonade.
We usually don't buy certain items until they are on sale, otherwise. Although now we have so many plums... I'm not sure that sales are always the right thing to pursue!