Reddit mentions of 8 Oz Plastic Cylinder Bottles with Flip Top Pour Spout, Pack of 6

Plan for the cold. Buy a good sleeping bag and don't scrimp on it. This link recommends Kelty brand sleeping bags. I own Kelty brand and its good. A mummy style fits closer for warmth, but can feel claustrophobic. a rectangular style fits looser for movement, but at a cost of less warmth.

Plan for warm layers for yourself. buying a good baselayer can help keep you warm when you're not in your sleeping bag. Merino wool is a good choice, but it costs. its worth the cost. there are synthetic styles that are cheaper.

Buy a good headlamp, because making your way to the public restrooms in the dark sucks muchly and you'd hate it if you dropped and lost your flashlight. plus carrying a flashlight in your hand means you can't carry much else.

Buy something that will help you cook your food and heat water. If that's going to be handled for you, then you might not need it. Me, I like to be self-sufficient and I really like my tea. Be sure to ask your group how food is going to be handled. I like GSI Outdoors brand because its nice and compact and its a nice size for a Vargo titanium alcohol stove. If you go this route, you'll need Denatured Alcohol which is hard to be shipped. Call around local hardware stores or hiking stores around you to see if anyone carries it. You'll also need flip top plastic squeeze bottles to carry the alcohol around in. Keep it in its own leak-proof bag. If you have a store close to you like Cabela's or REI, they carry this stuff too.

buy a travel mug with a cover. Me, I like Hydroflask brand because its flip-top cap is leak proof, but YMMV.

Here's a bunch of hacks that look interesting. You don't have to go all-out on these, but if you find yourself doing this type of car-camping again, you'll find them useful. Here's some more tips for first-time campers

WEAR STURDY SHOES. Boots are a great idea, but they also make hiking shoes that are lighter in weight. Buy merino wool socks. Merino wool is like ovens for your feet. I like Smartwool or Darn Tough

For food: I've done an entire camping trip on nothing but unrefrigerated foods. I bought a good crusty bread, squeeze peanut butter and squeeze jam. there are also pre-packaged hiking foods that are tasty. Make sure you bring several gallons of water and be sure to keep hydrated.

also BUG SPRAY! Don't mess around with "all natural" bug spray. You want DEET. I went camping in an area that was close to the water table and was basically mosquito breeding central. from the time when I arrived and the time I finally broke down and bought a DEET-based repellant, I was bitten 47 times.

edited to add: PHONE CHARGERS! This is mega important because power is going to be a premium at a festival. I own this Anker Power Core and it will re-charge your phone up to 7 times. Its kind of heavy, but its worth it. Anker also sells smaller ones that will recharge a phone twice to three times.

edited again to add: Anything you buy, test it before the trip happens. Sleep a night in your new sleeping bag. test your new camp-stove (outside preferably). cook something in your new camp pot. see how it works so that if there's something that doesn't happen the way you want it, you know about it before the big day. especially if you've never used a campstove before: you want to learn how to operate it without burning yourself or others or setting fire to things that shouldn't be on fire.