Multimeter, tape (Duct, teflon, electrical), cable ties, aircraft safety wire, fuses, hand tools, rock hammer, ratchet straps, bungee cords, air compressor hose for tires (I use my Air Lift air bag compressor), tire plug kit, spare receiver hitch with ball. receiver hitch pin, gloves.  Probably more in there but I can't remember.

I use one of these for storage and it's great!  There are numerous manufacturers making them for lots of makes/models of trucks.

I have pretty much the same tool kit, but use a tool bag which fits better into the back of my SUV and doesn't scratch it up back there. I forgo the drill and just use the hand crank for the jacks, and don't carry an extra hitch and ball.  I do add an IR thermometer for checking brake and fridge temps. My multimeter has a DC current clamp on feature to check charge and discharge currents. Teflon tape for water and propane lines, spare set of trailer wheel bearings, bearing grease, and a seal.  Also a quart of engine oil, a quart of automatic transmission fluid, a pint of brake fluid, and a pint of power steering fluid for the tow vehicle. And a 12V air compressor and good quality tire pressure gauge. 

Yep, a lot of stuff but I too have always got home OK. .