Prepping for a larp event:
Some simple stuff for getting ready for an event,
Garb: Comfort and style are everything. for a starting larper, sweatpants and a simple tunic will do wonders. (simple tunic, take a piece of cloth, 2 yards long. fold it in half, cut a head hole in the middle, presto, simple tunic. I would recommend hemming the edges so they dont unravel, but other than that, that and a simple rope belt and you're golden. For ladies(or the occasional cross dresser, Jae, I'm looking at you) you can get a nice flowy skirt and a peasant blouse.
SHOES: I cannot stress enough the importance of comfortable shoes. please, no sneakers. or if you have to have sneakers, plain black. Minnetonka moccasins look great, but they break down quickly and can be hard on your feet. consider taking a pair of tall moccasins and cutting the sole off, and slipping them over a pair of more comfortable shoes.
Salvation army or any thrift store is a good place to check for garb as well,
Weapons: If you have never made a weapon before, talk to someone who has. Trust me on this one, a poorly made weapon is worse than just ugly, it can be unsafe as well(I've seen a weapon that was made improperly launch a piece of foam half way across the field as the blade slipped off the pipe mid swing. thankfully, the wielder checked their swing before slamming the naked pvc onto someones head...) For your first weapon, I recommend simplicity.
Read the weapon rules to be sure your weapon will pass inspection. Some games allow fiberglass or graphite core weapons, some dont. some require specific pommel construction, some dont. just make sure that the weapon you want to use is safe and legal.
Food/water: dont assume that there will be something for you to eat at the event, pack a backpack with some noshies just in case. crackers, hard cheese, fruit, veggies, pepperoni, bread... all very period food, and tasty too. Bring water. A good eventholder should always provide water, especially on the hot days of summer, but to be safe, bring water.
Armor: there are many sites dedicated to the construction of good, safe, realistic armor. chainmail is easy to make, just time consuming. Please dont be that guy who duct tapes cardboard to a lasertag vest and thinks its cool armor. (yes, I really saw this at an event) additionally, while a leather jacket might actually provide some protection in a real world situation, its not period and wont count at most games. Simple guidelines are: Is it safe? does it look reasonably real? can you feel a shot through it? (this last one is a gotcha many times. SCA legal plate armor is not appropriate for a lightest touch counts system.)
No one expects a newbie at their first event to know all the rules backwards and forwards. However, there are some rules that all players are expected to know. the basics of the combat system, what the common combat calls are, what to do if you dont know what to do... (here's a hint: if you dont know how to respond to a combat call, no one will ever fault you for calling "Dead". dont be afraid to ask for clarification.)
Feel free to add to this list of stuff you need to know.