[How to do instruction] Making your Pi Read-Only

[TheOldPresbyope]

@Dorffen 

My experience is the same as Tim's but carrying an extra backup or two is always a good idea. If you've got the room then you might want to use a mini USB memory stick instead of a uSD card. IMO they're physically more robust, easier to exchange on the fly, and harder to lose in the heat of battle.  

Regards,
Kent