I've gone all over the place. Started with maintenance stuff, then got sidetracked by some good deals and ended up with a prinsu roof rack and cvt rtt. Then I did suspension, because honestly, I hate OEM toyota suspensions. I like a stiffer upgraded suspension. Then I did a bunch of interior stuff to fix things that annoyed me. Then I ran out of budget, before my maintenance stuff was ever done.
Now I've got my "big annoying things" taken care of, I'm taking more of a logical approach. Maintenance, preventative maintenance and preventative replacement of parts since I'm just over 200K, and building up recovery gear slowly.
I'm looking at big ticket items in 2 categories: camping, and vehicle. Camping is just that. It improves comfort or ease of camping, or ease of quickly getting out somewhere with short notice. Vehicle based would be things that improve and upgrade the vehicles ability to go places. Winch, armor, tires, etc.
Our next big ticket items are based on our family's experiences camping and our priorities. So, camping priorities are a 270 degree awning, and a drawer system for some improved organization of tools and kitchen stuff. Vehicle priorities are tires, hidden winch and winch mount. Then I guess we're going to either go down the electrical/batteries/lighting rabbit trail, or stick with some more basic armor add ons.
There's no formula for this. I'm explaining something my wife and I have come up with as we've gone out and camped and used our vehicle. So just do that! Take your vehicle, throw whatever camping gear you already have in the back, and go to a state park, or up some mild roads into some BLM or public land if you have some near you. Do a mild camping trip, take some notes, and make some lists of:
-Things you brought or prioritized that you didn't need
-Things you didn't have that you NEEDED
-Biggest upgrades or gear investments that you would most prefer or prioritize, or that would make your next trip easier.
Do this a few times, and your "build" however mild or extreme, will start following your own needs.