rough up the edge of a credit card and you could easily skin a rabbit with it, or you could order a taxi to pick you up
I once heard of an american guy who used a live .22 as a fuse in his truck, it got hot and went off, hit an artery in his leg and he died!!
We were trained in emergency first aid to use a credit card to seal the entrance hole in a sucking chest gunshot wound.Sticks right on and seals the wound through suction and allows the lungs to inflate.Dirty crisp packets out the gutter,going underneath a field dressing was always good to.You can always deal with infection later with anti biotics.
this was on a series of myth busters and was debunked.
i recon you could cut up the credit card and make it in to a pair of snow goggles (the ones with slits in) like these
the discoidal knife idea for the cartridge case above is a good one
the key i would keep for opening the door when i got home !!!!!!! or i might fashion it into a barbed spear point which ever came first