When NPCing you (generally) need a lot less stuff than PCing, but there are a few good things that I like to have with me whenever I LARP.
- Sleeping bag
-Air mattress/camp bed/camp pad, just something to put between yourself and the floor.
- Camp lantern or flashlight. If it's an LED one, put a bit of medical, or duck tape on it so you don't accidentally blind someone.
- Two pairs of socks per day. Just trust me on this one.
- Long pants and a sweatshirt / waterproof jacket
- Bug spray, and sunscreen.
- Hiking boots, or really good tennis shoes, try to bring a spare pair if able, cause wet footwear sucks.
- Hair ties
- A white sweatband/strip of cloth. It's the universal signal in LARP that you're not currently in game.
- Snacks. You burn a LOT of calories LARPing. I always like to have a bag of beef jerky, and a bag of dried cranberries with me when I LARP.
- A good in-period belt, even a plain brown or black leather one would do.
Everyone has different opinions on what you NEED when you LARP, and I'm sure I'm forgetting something.
This is less of a thing to bring (but it's definitely not a bad idea to bring along), and more of a general tip: Drink lots of water. It's pretty much impossible to drink too much water at a LARP.
I haven't been doing this as long as some other folks, so they might have some better advice than me.