Iam a vet and find that alot of the equipment i carry ties into my work eg.
Mobile phone-can ring clients-vica versa
Wave-cutting ropes and to hgold animals still in the field etc.
AAA maglite-for looking into animals mouths, eyes, opther dark places, possibly there accomodation.
Carabiner-for holding things or attaching things-aniumal leashes to a holding point, holding spare equipment in field surgery.
whistle-is purely for survival
Resusitation pack-has spare pair of latex gloves which can be used if i'm on my own and my current pair split. i also had a owner have a heart attack on me!

You see what i mean!

Mark