I've seen some excellent lists on this forum for the pilot, glider,
and landout/emergency kit. I'm wondering if anyone has developed a
list for the tools, parts & materials to always have in the tow
vehicle. I need to assemble a single toolbox that I can transfer
between tow vehicles (I use a primary and two alternates).

Easy to start with:

Screwdriver(s)
Electrical tape
Wire, wire cutter/crimper, heat shrink tubing
Pneumatic tubing and connectors
Gaffer tape (awesome stuff)
Scissors
Multimeter
Fuses
Yaw string
Extra catheters
Lighter

What am I missing?

2NO (yeah ... software guy)