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.
Yes, I do this too. Depending on what else I'm carrying, I'll put my stove and cooking cup in there (except on long trips when I need to cram every cubic CM with food).
Since I have the Bearvault 500, it also makes a good chair when there's not a convenient boulder around. I stopped using my 450 even for small trips because of this. I just fill it up with other stuff so stuff doesn't rattle around too much inside.
