After 15 years and 350,000km.......I had to have a good think....
A good head torch, plus a spare......
Good tools
Binoculars - I didn't know how much I used them until I lost them!
We do 90% wild camping, so I carry special manhole tools and rubber gloves.....
Also a complete set of water tap adapters and a long hose. Same for electrics - I have all the adaptors and a 50 metre reel.
I converted to refillable gas bottles a few years back, and it's been great, but you have to plan your fillups depending on which country you are in.
We like to stay in one place quite often, so we have lots of
battery power and a good
solar panel.
I finally found a small Honda suitcase generator on Ebay at a decent price.....have only used it once or twice a year, but every time it's been a life saver.
And finally - I am a technology fan. My GPS is stuffed full of POI's and the first thing I do in a new country is get a local data sim card. I use Google earth to zoom into wild camping spots - it's absolutely brilliant. My Macbook Pro is the only thing I would save in a fire!
Have fun!