I had a car lift for 10 years or more and I could not be without these cars a pain to get under ...another tool is a rechargeable air compressor about the size of a drill take it anywhere you want. And a battery powered half-inch impact. And a floor jack on rollers this is a short list of tools I could not be with out anymore. What got me thinking about this was how Jumping a car has changed in 20 years jump boxes are little tiny things now with lots of power. Of course there are other things like a lockout kit. I had to use that once this week on an XJ8. And how flashlights of improved in 20 years..Feel free to add in on some of your favorite tools for these cars.tire plug kit,ect

 

My 1ft long LED work light stick
Also, any power tools. Electric ratchet, cordless screwdriver, cordless impacts both tiny and large. Sure you can get by without them, and I did for a while, but they just save so much time and strain on your body.
Lastly, to go with those power tools, impact rated universal joints. Somewhat awkward with hand tools but a breeze with power tools

EDIT: safety glasses and sound damping earmuffs. Earmuffs for power tools, safety glasses for working under the car. After getting a speck of rust once caught in my eye for a week, never again.

 

If I have to hook up to my car trailer. I always grab a floor jack my half-inch impact and a set of deep sockets my impact has a matching small air compressor looks like a cordless drill. Of course they made a matching flashlight .. so you can use the same battery. I was hauling a car back two summers ago and blew a tire took about five minutes to swap. After that I learned my lesson something else I’d like to keep in the truck is the plastic tool kits you can actually get a lot done with just a kit... it just made life easier with some of these tools. I took a winch and spun it around backwards then mounted it on the car trailer that’s a lifesaver

 

I hear you on the lift. I bought a lift in 2007, about five years after I built my shop building and then wondered why I hadn't done it sooner. Another tool, or piece of equipment I couldn't live without is my blast cabinet (and required 60 gallon compressor). After years and years of wire brushes, wire wheels on a drill, steel wool and sandpaper, no more. Fill the blast cabinet with a bucket of glass bead and parts are paint and rust free in seconds. The only thing I did wrong was the first one I bought was too small. And the replacement is still really too small. I'd like to have one that I could get a 15 inch wheel inside and still have room to blast every angle plus an even bigger compressor so I wouldn't have to stop and wait for the compressor to catch up. But kinda limited on space.

As for just small hand tools, Gearwrench, especially the stubby ones. Modern Jaguars are so tight there's most places you can't swing a standard ratchet or even get a get a 12 point on a hex. The 5 degree swing arc has been a godsend. Also their 120 tooth double-pawl ratchets with 3 degrees of swing.