When you drain the tuna

The liquid from canned tuna can be saved in the freezer until you have enough to add to soup or use as the liquid in white sauce. Bits of tuna will be in it and may be enough to flavor the soup, or you can add it to a smaller can of tuna than you usually use for cream of tuna.

"Free" cooking oil

If you buy tuna or fish steaks in oil, drain it into a container and use it in stir fry or to fry potatoes or saute other foods. No sense in wasting it; it's good oil for cooking although it might have a slightly fishy taste, so be judicious where you use it.

Cheaper than canned salmon

Make a fish loaf or patties from canned jack mackerel or tuna instead of more expensive salmon.

There's more to canned food than food

If you use food from cans (and who doesn't, now and then, anyway), don't just toss the can when it's empty. Whether it's a small can, like a tuna or cat food can, or a large one, the label is paper. Tear it off, trim the ragged torn edges and there you have a piece of paper for lists or notes.

Then wash and use the can to hold other things from candles to pencils to paint brushes. More on tuna and cat food cans later.