Are you talking about the big cans that are like a soup can or the short cans like a cat food can?
I buy the Innova 5.5 oz short tins and keep them for 4 days in the fridge. I give Chester a big spoonful (about 1/4 of the small can) in with his dry and we finish the small can in 4 days normally.
If you like the larger cans of food I suggest you make single-serving portions and freeze them. That way you don't waste anything. An easy to do that is to put big dollops on a cookie sheet (just like you're making cookies) and stick the whole cookie sheet in the freezer and then when they're frozen you can put them in a ziploc bag. When you need a portion just take one out and defrost it in the microwave or leave it in the fridge overnight to thaw. I make single-serving portions of canned pumpkin using an ice cube tray and so I always have pumpkin on hand for those "soft" days.
"My little dog: A heartbeat at my feet."