Hydration is key.. I usually just had water and kept the sugar/salt packs from the field rats and added to my water if I needed a boost.. Obviously physical fitness helps a lot also. Some of the things I kept in my TAC or ruck for ex's were proteinbars/energy bar..chocolate bar(by the time I ever got to eat it usually melted and not very nice but did the trick).. Red bull or two.. Last by not least Tabasco as most of the feild rats were pretty blah.. Mind you if your doing a 24hr game and are in possession of food and your in a QRF or trying for a lil Shuteye keep in mind racoons are very mythical creatures and can drag away the 40lbs of rucksack your using for a pillow
Had to edit because I forgot to mention.. 24hr game w/ lots of walking (possiblely wet terrain) pack spare set of boots and at least 2/3 pairs of socks + some foot powder.. If you happen to get your feet soaked 2hrs in the rest of the 22hrs won't be so fun..