Why not simply use a cooking pot and tape the lid on? Someone wrote a while back about how we all like to improvise when there is no need to. If all you've got is a Sig box ok, but why chose to use the wrong thing when you can pack a real cookpot? Or slap a kidney shaped mug on the bottom of your water bottle.
Basically, weight.
This is semi-EDC, and not for when I expect to have to use it. A cooking pot would (I expect) be heavier, and would not be large enough (in its longest dimension) to act as container for the other items, hence the weight of a separate container and a two-piece solution.
It's more a substitute for aluminium foil or a collapsed disposable baking tin than for a cooking pot. A lightweight metal mug would be another option. The steel ones I have are too heavy, and it would still be another item.
I don't carry a conventional water bottle, but there's a ~1 litre platypack in the tin and some roasting bags that can also be used for water storage.
eeph