Got to ask yourself, what do you need it for? In my previous job, space was paramount so I carried a small tin (tobacco sized) sealed with tape. In it was stuff that addressed, loosely, the priorities of survival, stuff like asprin, safety pins, candle, lighter, razor blade, torch and puri tabs. This was augmented by pocket contents (knife, hat, gloves, compass, etc) and finally a small day sack with the 'luxury' items (goretex, etc). That way, I always had something of use on my person. Now space isn't at a premium, I carry pocket contents (modularized to the environment) and a day sack. If you are to carry a tin, here's my thoughts:
1. Should be on your person at all times (therefore small and waterproof). If you carry it in your jacket, and regularly take your jacket off, what's the point?
2. It should contain items not easily made/obtained in the wilds.
3. Items, where possible, should be multi functional.
4. Take it into the woods for one night with cock all else. If you survive, well done, you got it right! But if you think 'no way', then again, what's the point? Only miniturize and scrimp if absolutely necessary. "Any c*** can be uncomfortable..."