Stuff that I've used that I don't think I could live without now:
1. Thermarest Neo-Air: you can't over-value a good night's sleep!
2. Rangefinder: estimating distances in the mountains is a mug's game.
3. Trekking poles: they'll save your knees.
4. Baby wipes: self-explanatory
5. Kifaru gun bearer: way easier on the body than slinging your rifle over your shoulder, and way quicker to get into action than having it strapped to your pack.