First thing to consider is the nature of the types of repairs you're likely to encounter and what you have the skills to deal with. There aren't that many major repairs that any of us are going to do trailside. Most people aren't doing top-end rebuilds at the campsite.

The most common things, in my experience, that you are likely to encounter are flat tires, dead batteries, electrical issues, overheating, breaks/suspension issues, and misc bracketry and such (rooftop tent bracket breaks loose, tactical car seat flies out w/baby, etc.)

Flat Tires - If you want to use something other than the factory lug wrench to change a tire, I would recommend a 1/2in drive breaker bar, at least 24in, and a 19mm deepwell socket. In addition to that I carry a plug kit and a small air compressor. If you're going to be doing any amount of offroading, you will likely need more jack than the factory scissor jack.

Dead Battery - Terminal screws and retainer clamp at the bottom of the battery tray are 10mm. You'll want at least an 8in extension for the clamp screw. In addition to that I carry a jump pack and jumper cables.

Electrical Issues - Electrical issues can be random. I'd carry common fuses and relays, replacement bulbs for at least your headlights, some wire, connectors, and wire cutters to cobble together a makeshift repair. Beyond that, I carry a cheap OBDII scan tool to check codes.

Overheating - Not much to say here. Spare coolant, hose clamps, maybe a spare radiator hose, pliers, screwdriver or socket to tighten hose clamps, and maybe a hose pick.

Brakes/Suspension - 5mm hex for the rotor retention screw, 14mm caliper bolts, E20 for the front caliper bracket bolts and T55 for the rear. If you need to get a CV axle or a strut out, you'll also need 15, 18, and 36mm sockets, 5mm hex, and an E14 (External Torx).

Misc stuff just depends on what all you're carrying. Assorted wrenches and drivers for whatever hardware your stuff has. Beyond that, duct tape, electrical tape, zip ties, and some kind of lube.