I do quite a bit of camping and combo camping/fishing trips and here's a few things I wouldn't be without:
Headlamp - When setting up your tent in the dark, or doing just about anything else that takes two hands, a headlamp is invaluable! If you have a red filter, bring it. Otherwise, you can use a red plastic bag or something like that. I misplaced my red filter and that's all I do is use a little red bag that came with some random thing I bought. This way you won't ruin your night vision. And don't forget the extra batteries, even if you put in brand new ones. More than one person has had a flashlight turn on in their bags and kill the batteries.
Swiss army knife or Multi-tool- Pretty obvious why this is needed. Bring the multi-tool if you have it instead . The pliers can be a huge help.
Plastic garbage bags - Throw a couple of these in your gear. Whether it's using one as a poncho, or using it to throw wet gear in on your way home, they can really come in handy. They also take up pretty much zero space and weigh nothing so there's really no reason not to bring them.
Chap stick - Another must have, especially when wading in hot, sunny conditions for days. You can also use it to lubricate a reel in an emergency. Just remember to clean it when you get back!
First aid kit - I hope there's no need to explain why this is a must-have!
Bug spray - Use the stuff with at least 25% deet.
Duct tape - The original multi-purpose tool. Some places sell small rolls of it, or else I'd just buy a roll and cut 1/2 of it off to save weight and space.
Rope - Bring along a 10' piece of nylon braided rope, you never know what you can use it for.
Wire - Bring along a few feet of lightweight wire. Can be used to fix a whole lot of stuff from broken kayaks to broken reel seats to broken guides and more.
Medicines - Take a small medicine vial and pack it with a variety of different medications including aspirin, allergy, anti-diarrhea, Tums, and any others that you normally use.
Hydrocortisone cream - As somebody that gets poison ivy (or poisonwood in the tropics) extremely badly, this is a must-have. It's also great for those sand flea bites.
Nylon zip-off leg pants - If you don't own a pair of these, then buy one. They're one of the best pieces of gear for the flats/tropics you can get. You can wade in them and protect your legs from the sun without being hot, and they'll also protect you from the sand fleas and mosquitoes in the evening. And you can take off the legs if you want to wear shorts and throw the legs in your pocket since they're really small and lightweight.
I've also attached a list that I've put together and expanded on over the years that is my standard list that I review for all camping and fishing trips.
My passion for catching fish is eclipsed only by the fish's passion not to be caught.