A one-quart freezer bag. Unless you're carrying a kit for a group, the probability of an emergency you can't improvise for in a party of one or two is extremely small. (A Wilderness First Aid course will teach you how to improvise!) My "emergencies" consist of small cuts and the occasional dreaded infected hangnail, requiring bandaids and a small amount of antibiotic ointment. I'm also prepared for blisters, although since I switched from boots to trail runners, I haven't had any. I've encountered a sprained ankle exactly once in 70 years of backpacking and horsepacking. I was prepared (it happened a week ago Saturday), but now I need to buy another roll of veterinary wrap and add duct tape to my trekking poles to replace what I used on my grandson (who is almost completely recovered). The duct tape over vet wrap worked extremely well, BTW.