just to add to the lost above some of the items I take:
meant for your inspiration, not meant as intimidation - sorry the lost got long, but these are things I have carried along at least once in the past 15 years . . .
not all at the same time, and not all in every wheeler we have - decisions what to take adjust to distance of travel, extent of wheeling, particular vehicle involved, anticipated group going with me, and sometimes plain laziness (when close to town)
I generally carry info on confirmed infrastructure or support businesses along the way, AAA emergency contacts, insurance information
- big hedge clippers (when in the 80s, for sure) - ACE has them for ~$60or so
- zip ties of multiple sizes (every vehicle)
-tire pressure gauge - and I like to take tire deflators, too (get the Stauns over the Amazon el cheapo offers, trust me)
- air compressor - onboard or portable (every vehicle, unless I know that I will definitely be able to smooch off some source when I drive the 40; or I take the portable MV-50 that has served me for more than 15 years by now

: - got a brand new one for the GX, too)
- velcro straps (the computer cable ties of various lengths you can get cheaply at ACE)
- multimeter (and assorted fuses specific to the vehicle and general wiring parts - carrying fuses for other vehicle types in the group has also come in handy in the past

)
- tie-downs for all the crap in the rear (of the 80s and later models; need to develop a new system since the rear bench in the 40 that was holding down everything went away . . . )
- blankets (moving blankets are cheap) to cover stuff when parking/camping in sketchy areas, and as general theft prevention, as well as simplifying with the general tie down of stuff when you throw them over everything
- spare brake fluid (on longer and more remote trips; the stuff is corrosive, so wrap well and spill-proof)
- spare tranny fluid (when in the later models father away from town)
- octane booster (for those of us with S/Cs

)
- ARB airline repair kits (for those of us with ARB lockers; on longer trips, I also carry spare solenoids)
- baling wire and double-sided tape (both of which have come in unexpectedly handy on later model trucks, go figure

)
- assortment of bolts, nuts and washers - springs for the carb (and choke on the 40)
- WD-40, moly grease, regular grease, grease gun
- knuckles studs - search on MUD for stories about those . . .
- on long trips with the 40, I carry axle shafts (prepacked with moly-filled birfs); I used to carry a steering box, too (but now need to develop a new parts list since getting power steering)
. . . and more . . .
and don't forget a comb - yes, a plain haircomb: this comes in handy when your kid managed to jump at the cholla before the plant had a chance to expel its buds on its own terms (and then the kid panics, swirls around and pics up more buds, and on it goes . . . followed by an hour of misery for all involved

), or your dog walks into the stuff, or your husband is too focused on the camera and sits down on the proverbial mother-in-law-chair (but fun was had by all

), or you meet an ATV rider who flew down a dirt road way too fast, missed the corner, and landed like a ragdoll with all kinds of body parts into plants with thorns, spurs, hooks (she broke two front teeth in the process)

and so on . . .
a good medical kit would also help - I am in the process of assembling a kit that goes beyond the Toyota/Lexus kits, since we have found them somewhat deficient on the trail . . .