Camelback is convenient, but not imperative... what's nice about one is that it can balance the weight on your chest rig, vest or pc front/back depending if you wear a lot of stuff or not. As long as you can carry it on your gear, you don't need a camelback.
Neck protection... not super important, the face protector is more important as your teeth are valuable.
Flashlight.. handy to have.. not necessary unless it's a milsim that goes deep intot he night. It could be considered a safety item though so it would be a good idea to have some sort of light with you if you are playing in the dark. Same with radio, an frs one is handy, or a whistle if you're playing in the bush... if something ever happens you need a way to be found.
I kneel a lot, so I need kneepads... depends on your play style and your tolerance for pads that may or may not stay where you put them.
Gloves are handy for the same reason that neck protectors and pads are handy. But not a necessity.... but being shot in the knuckle sucks.
Unless you are doing a multi day field op in the middle of the ass end of ass end of nowhere's ville, a compass is useless. If you get lost, a whistle or radio is more handy.
same with binos... usless unless you're at a bigass field op. Use your eyes. Your guns can't shoot farther than you can comfortably see anyways.
paper and pencil are handy for milsims or games with passwords, taskings, problemsolving puzzles and whatnot... not super useful in a skirmish.
Only you can answer your battery question.. How much do you shoot? Can you charge on location? Same with mags. If there's no limit, carry as much as you care to carry for 12 hours. If there's a limit then go with that. I generally have spares that I leave loaded at the CP so I can get back out in a hurry if needed.
Bring snacks and 1 meal. or enough snacks to last you 18 hours. Why 18? cause you're going to be AT the location at least that time. Arrive, shoot the shit, bomb mags, register, chrono, brief, etc.. shit takes time. Same with after the game.. police your garbage, organize your shit, pack your shit, etc.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.