I used to do a fair bit of outdoorsy stuff, and I could probably type a bunch of nonsense but I'll try and keep it short.
Keep your foodstuff nonperishable. You won't have cooling past the first day, barring daily trips to buy ice (which is scarcely camping at all if you ask me). Bear in mind you'll be expected to haul all your trash out with you, so cutting down on packaging pays a lot of dividends. Canned stuff is fine, just make sure you have a can opener. You'd be surprised how often that gets forgotten.
A utility knife is a wonderful thing. A proper Swiss Army knife is nice but possibly spendier than you'd like, so a cheap one might do you for the first trip. Even just being able to make some kindling makes campfires that much easier.
BRING BUG SPRAYS. Also sunscreen. But really, a first aid kit and some basic things to deal with bugs and sunburn. If you're uncomfortable early on, it's going to be five days of misery and you'll hate it and lower the overall mood. There will be bugs, and you are going to get bitten. Bank on it. Your organizer might have this covered, but you'll feel a lot more smug if you can take care of yourself.
You should also have some sort of container you can bring for your own drinking water. Canteens are nice, but even just a fannypack you can cram a sports bottle into will save you hassle.
Bring a flashlight and something to read, too. You just never know if you've got a bit of time to fill.
Before I type more, you should really see what other kit you're going to be set up with. At the least, you'd want a framepack to lug everything with, a sleeping bag, a mess kit (a compact set of dishes), and the things I mentioned above.