11. Put A Severed Body Part On Ice
With the wonders of medical science, cutting off a finger doesn't necessarily mean losing it forever. Unless you follow advice from the movies, of course.
It is true that you should keep a severed body part cool, as a cooled part will be viable for reattachment for 18 hours, compared to the 4-6 hours of an uncooled part, but putting it directly into ice will scupper any reattachment plans by damaging the tissue further.
Direct contact with ice will likely cause freezer burn and frostbite - you know, that thing that causes people to lose body parts. The best advice is to gently wash any dirt and contaminants from the part, wrap it in a clean, damp cloth, place in a sealed plastic bag and suspend that in ice water.