I've carried a mini-shield and a pair of gloves on my keychain for at leat 10 years, was a volunteer firefighter/EMT. I used the MDI CPR microshield, removed the paper liner/direction sheet and refolded the shield with a pair of nitrile gloves wrapped around it. No more bulky than the original package, about 2x3, and 1 inch-ish thick. The bad news is without the paper wrapping the shield seems to crack on the seams a bit sooner, but I still got a good 3 years out of them and did not have an issue replacing them for 8 or so bucks. Used it once, was glad I had it with me instead of in the car or somewhere else, can't beat having it on you when you're out. On the keyring pretty much insures you don't have to worry about sticking it in a pocket or whatever. Space in the pocket was no issue with cargo pants, but is at a premium in jeans.

Gloves were used way more often, happened upon plenty of vehicle collisions in the course of driving around so I found the gloves pretty useful.