Well, I guess there's some supplies in the tin, since I can't remember what I was thinking. I think there's probably a very fine needle with a spool of thread that matches Mouse's clothing color, in case of rips and tears to what she's wearing (And possibly in case she needs emergency stitches). There might be a small amount of bandages, and maybe a rag that can handle being boiled (If she needs a liquid disinfectant, that's a little to difficult to carry, so a disinfected rag and boiled water is enough, maybe)
Does this sound okay?