Reddit mentions of SUAOKI Led Camping Lanterns for Lighting (Powered by Solar Panel and USB Charging) Collapsible Flashlight for Outdoor Hiking Tent Garden (Emergency Charger for Phone, Water-Resistant)

Arm sleeves - These are great year round, the more you sweat the cooler they get.
Bluetooth Speaker/Charger - If he's in an LLV and the outlet doesn't work this doubles as a charger, I've been using this for over a year and the speaker is loud and last for over 3 days.
LED rechargable lantern - These are great during the fall/winter months when we're out late, I clip it to my satchel and it illuminates my entire body and a decent area around me so I don't fumble with a clip light on my cap. Plus if you do box deliveries you can clip it to the top of the door and see pretty damn well.

You mention air-mattresses so I assume you're just car camping, not hiking? Probably a good choice for first-time camping.

REI has a good checklist here. You obviously won't need all of it (like navigation stuff), but it's a good starting place.

Tents are a bit tough without more detail. Are all six of you planning on going in on purchasing a six person tent? Do a select few people want to buy 2-3 person tents to just keep? Are you planning on hiking in the future, in which case you'll want lighter tents - at more upfront cost? How many sites have you reserved? If only one site, there will probably be a limit on number of tents you can have.

Either way, some good starting places:

• ALPS Mountaineering offers a 6-person tent for $140, and is a well regarded brand on here. That's about $24 each.
  
  
• REI also has a good 6-person tent for $150, and this subreddit loves REI (and deservedly so). Can't go wrong with their gear. About $25 each.
  
  A tarp for the tent might not be necessary, but is something worth considering if you're worried about wet conditions.
  
  Air mattresses are an unnecessary expense if you're on a budget. Pretty much any sleeping bag that's not designed specifically to be lightweight will have enough fluff in it to provide some padding. Something like one of these big fat ones for $25. You're camping anyway, not staying at a hotel. A few nights on the ground won't kill you. Bring a few thick blankets if you're worried though. A good inflatable pad will probably be more than you want to spend money on.
  
  You can forget backpacks for now if you're just using your cars at a state park or something. A good pack is expensive anyway. But a duffel bag or small backpack or something is a good idea to carry clothes, food, and supplies. Doesn't need to be anything special.
  
  One important thing to keep in mind is firewood. Don't bring it. You should always buy locally (most parks will supply/sell it) since this prevents the spread of dangerous pests like Emerald Ash Borers and such.
  
  A few more basics you'll want:
  
  
• A first aid kit, probably. Even at a well developed state park, it's still a good idea to have one nearby for smaller injuries.
  
• Some sort of firestarter. Doesn't need to be fancy. Just, if you bring a lighter, make sure you have fluid for it. Something like these guys might be useful though if you're not used to starting fires.
  
• Flashlights/Lanterns are useful. Something like this or this
  
• A cooler.
  
• A pillow. For car-camping a normal pillow will do. Just make sure you don't forget. I always forget a fucking pillow when car-camping.
  
  Food. Personally, I think planning and packing food for a camping trip is one of the best parts. There are more camping food "hacks" and ideas out there than you can imagine. Plan it right and you'll eat better when camping than your average day in the college dorm. A little bit of tin foil, pie pans, and prep the night before and you can eat stuff like this or this or this. Just browse and look around until you see something that makes your mouth water. Most of it is no more difficult than throwing ingredients in some tin foil, and then throwing them on the fire later (in some cases you'll want to pre-cook chicken or fish or beef though).

These are relatively inexpensive, but cool to have items:

Long Handled grill basket

Collapsible solar light

personal water filter

Haul and hang kitchen organizer

Daypack There's nothing special about this particular one, but every car camper needs a daypack for hiking.

Battery pack for charging small electronics

Weatherproof matches

Hiker's Emergency whistle

Mosquito head net

Hydration bladder

Collapsible water jug

Condiment squeeze bottles (for more efficient cooler packing)