1) Buy in season.
2) Look for deals.
3) Buy in bulk.
4) Buy the tougher cuts of red meat (eye of round, shoulder), and braise them. The cooking takes longer, but they're much cheaper.
5) Buy whole chickens, cook the entire thing up, and then shred it.
6) Tuna, whey, milk, eggs.
7) Make bigger meals (such as stews, casseroles, etc) and keep it in the fridge for leftovers, quick grabbing, etc.
8) Buy meat close to it's sell-by date, or on the sell-by date. It'll be reduced super cheap for quick sale, and you can portion it out and stick it right away in the freezer to cook up whenever.