I suppose this is more of a weapon issue, but seeing as how this also about 24-72 hour gaming, it sort of applies here.
How to see, live and fight in the dark. Without the specifics of lights, lasers, NV, etc., these are absolutely essential items, with relative scale of usefulness that depends on your gear. If you carry all that, you must also carry the support systems, which take weight and volume your pack must accomodate. Things like your nice PVS-14 is risky to simply toss in your pants cargo pocket during the day, but a nice Tactical Tailor hardcase and tossed in the pack is preferrable.
Then, you need a weapon light, you should not be shooting your gun if you can't see down the barrel, a core tenet of airsoft that needs to apply in daylight and darkness equally. No weapon light = blindfiring. Now, you need batteries for that light. As well, everyone should have dead lights and handheld lights, all taking batteries.
Radios, extra batteries as well.
Charging systems. One might look at simple storgae devices to recharge as needed, or solar chargers to attch to your pack during the day. It has long been a problem for warfighters to carry portable power-using devices and keep them going without resupply and carrying heavy batteries. I have a problem with this, as LED lights with visible and IR capabilities are expensive, and incandescant is so much cheaper, but with increased battery consumption. It is an angle I am still working on, but IR is a must when you use NV.
Boots. Long duration games mean lots of walking. Far more important than any other item you will wear.
Socks. Never had more than one pair. Never needed it. Crossed rivers and puddles more times than I can count.
Water. I have in the past always carried my water on me, usually just a bladder. Last year, I got into filtration. MSR ceramic-element filter, with Aquatabs for pathogen. Green Nalgene bottle for unfiltered, clear bottle for filtered. Haven't needed yet to actually use it in-game, as I have only once ran out of bladder water, and that was many years ago. But it sucks when your slurpy buddy blasts through his 2l bladder just so he can piss clear, and weasle off your supply.
Back to tenting. I bought a large tent (Snugpak Bunker) that will sleep 3 Brits or 2 North Americans, and had planned to use it this year. However, I have come to the conclusion that sharing equipment is a bad idea. I lean more towards individual self-sustainment. If your buddy has the tent a mile from you, you are not tenting, and if you are carrying the food, he is not eating. So, I tailored my gear for individual use, and have encouraged my team mates to do the same, although nobody has put much effort into yet that I have seen (2 PTWs but no sleeping bag