Some great stuff has been offered up but I'll add my 2 cents.
Enough water for the day, I go 1 litre per 2 hours activity and it's been working.
Those baby food meal packs, not in glass bottles but flat pack. Not the tastiest stuff but packed with everything you need and highly portable/quickly consumable.
Wet wipes, a God send if you need them. Hand sanitizer as well.
Duct tape binds everything.
Layers for clothing, lots of info out there on how to do this. Consider a boonie cap versus a helmet if it's very sunny.
That's about the main things, I pack enough batteries to not worry about charging... way more convenient then charging in a field.
Always remember you can keep most of this at you base/respawn... a lot of new players (myself included) carried a buttload of too much shit and burn out way to early in the game. Pace yourself, drink all the time, find lulls in the action to sit/lie down.
Is it our game you're coming to?
EDIT: lights are super important, but so is light discipline. A red filter would be good to turn it into a kill light.