You can always put things besides food in the canister, right? On week long trips mine is packed tight with food and lashed to the bottom of my pack, but by the end of the trip it is inside of my pack with things like the trash and dirty laundry, my head lamp and stove, etc. And besides, the overwhelming majority of the canisters on the market fall within one or two size ranges because most people just won't buy more than one. Even a retailer as big as REI stocks more than one brand, but essentially only in one or two sizes.
