You're right with the Tuna, Hayes. What about Baked beans?
I'm in a similar position, being a student. I don't know if this is prqactical for you, but I always check the dates of the chicken breasts in the local Iceland...I've worked out their pattern for reducing their stock that is approaching it's sell by date. Typically, I get 500g of Grade A chicken breast for £2, but have had it as low as £1.25. I load up on cheap meat and freeze it. Good for reduced steaks and Pork, too.
I'm always their first customer in the morning, then back by 11am for the next round of cheap stuff. Then it's off to Sainsbury's at 8pm for 30p packs of doughnuts, £2 birthday cakes, and £3 chinese meals for 2.
F*ck, now I've got a girlfriend where's the incentive to stay lean?!
