12-hr is too short to pack MREs - chocolate bars, muesli bars, etc are far more useful especially if you are on the go a lot.
MREs are only useful for 24+ hr event where you actually get to sit down and heat up a meal in your rest/down time. Since it is a 12 hr event, and presuming that it is a non-stop event, time to heat up and eat MREs is a waste of valuable game time.
Be an energy-drink/caffeine-addicted squid!
Personally would just focus on thermals that you can layer up (fleece, waterproof softshell, puff jacket) + extra consumables (bbs, gas, batteries for lights and guns etc). Even with thermals, you'll be surprise how warm you'll get underneath your kit on the move.
12 Hr is too short for sleeping breaks. I've done multiple 24-40 hr events where I only get 2-3 hr sleep anyways.
Last edited by Amoki; May 2nd, 2015 at 18:08..