I use badge holders with a ziploc like closure. Waterproof and easy to update.
I use it both to identify what it is and to mark equipment that has some important notes to it:
- Avalanche airbag: Attach canister (stored loose)
- Avalanche transceiver: No battery (stored separately)
- Things that need maintenance
- Things that are broken.
Good idea - I may leave the backs blank and white; and use a dry erase marker to make notes.