The F250 I drive has an extended cab. The back part of the cab has two jump seats that fold up when you aren't using them. I can fit a complete sea bag ( I think the Army calls it a duffle bag) back there.
Once Spring comes I spend a lot more time in the woods. This part of the mountains is honeycombed with old forest service roads. Further to the west of me, there's a big wildlife management area where you can drive into the forest and never see another human being. This is where I slipped a tire over the edge of a clay bank and got stuck out in the forest some years back. I got lucky that time and some kids in a big four wheel drive truck with a winch came along and pulled me out. Since then, I've been more conscientious about what I take in the truck when I go out in the woods.
Here's a description of what I take out there now, regardless of how long I plan to be out or how far into the woods I'm going.
I take a good sleeping bag. I have a tarp big enough to cover the truck bed, with tie downs. I can put the sleeping bag in the truck bed, latch that tarp down, and I'm fairly well protected. If there's the possibility of rain I'd have to cut a pole and secure it to the pintle hook in the truck bed to give some "slope" to the tarp, otherwise I don't bother. I also have one of those little bubble tents that comes in a hand carry sack. Mine is camouflage. I know this is not smart, and it should be orange. I just prefer something that doesn't stick out a mile in normal circumstances.
I have an axe in the truck. It stays there year in and year out. I keep one of my very good Kabar knife clones in the bag, and I always have a folding knife in my vest.
I have a plastic storage box from Walmart with snap down ties. Inside that , there are matches, a lighter, spare batteries for my GPS, flashlights, LED lantern and my hand held transceiver. There's a small LED flashlight and a big police style flashlight. I have a Coleman LED lantern and a smaller little LED lantern I got for $5.00 a long time ago. I put some of those small fire starter sticks that come in waxed packages in the box because they will light even when it's wet.
While I don't keep a rifle in the truck at night, I do have a cloth gun rack I got from Sportsmans Guide years ago. It hangs on the back of the truck seats, and you can slip two long guns in there. I usually have a rifle and a shotgun if I am going out "booney crashing." I keep spare ammunition for those in a smaller plastic storage box, along with 9mm pistol ammunition.
Strange as it may sound, I keep a flare gun and six flares in the sea bag. These are the relatively small and inexpensive units you can buy in the sporting goods department at Walmart. Especially in summer, the foliage is so thick that anyone looking for you from the air would never spot you under the canopy. For that reason, I keep the flares and four smoke canisters. Having gone down the bank once, I know I could roll the truck and if I do I'd like to make it easier for someone to find me.
I have a little cooking set I bought at a camping store. It has several pots nestled into the largest, but it's still very compact. I also have a two cup metal percolator. With these I carry along an old army mess kit, one of those that can fold into a frying pan if you need one.
As far as food, I take a bag of dog food. It stays fresh because I replace it and feed the older bags to the dogs. For myself, I take canned bacon, rice, and five or six miscellaneous cans of whatever looks good. I bring coffee, because sometimes I like to just stop, find a place with a nice view or near a creek, and brew up. I have a 5 gallon jerry can of water, but the woods are alive with small creeks and springs, so that's not a real issue.
I have a very basic medical kit in the truck, not huge but sufficient for things like cuts.
Naturally I keep a good chain, with a decent "come along", and a shovel in the truck. Carrying room is not a problem and the old maxim "better to have it and not need it than to need it and not have it" comes into play. Having watched untold hours of Cody Lundin, Les Stroud, and the Hawkes you get a feel for what would be "nice to have" if you had some misadventure in the deep forest.
What I try to do is think of what I would want if I was intentionally camping. Then I bring it along. If I'm not doing anything more than just a day trip to the woods, no harm done. If something goes wrong, then "prior planning prevents poor performance."
I don't actually have to drive to be in the woods, but it's nice to get out away from the house. Here's an air photo of my place, which will show you what I mean:
I don't head out into the woods as much a I used to when my son was at home. He and I enjoyed going out and just finding new places. Once we found an old forest service camp ground that had been closed in the 1960's. The buildings were all falling down, and it looked like the set of a post apocalyptic movie production. We hiked into that place, and I don't do much hiking anymore. But thanks to all the old forest service roads you can get way back there and haul all the comforts of home with you in the vehicle.