Tools in my boot... In order of importance
Quality ratchet screwdriver and one of those rubber packs of security bits (contains the all important Torx bits)
Spider wrench (can store in the spare wheel)
Quality socket sets - 1/2" and 3/8"
Decent pliers
Flat and crosshead (not pozidrive) screwdrivers, including the mandatory BIG flathead which always ends up the most often used but never turns a screw in its life
Big hammer
Set of metric spanners, including 15+16mm (one of those is used for engine mounts and often isn't included)
Mole grips
Allen keys
Knife
Breaker bar
Torque driver
Gas soldering iron
Multimeter
Plenty of wire (not just for carrying electricity)
Zip ties
Jubilee clips
Trolley jack
Ratchet action axle stands
Cordless drill
I tend to carry most of that around with me (minus the drill, jack and axle stands)

but thankfully the worst I've had to do at the side of the road away from home has been to change a tyre and hack a throttle linkage together
When I need the boot space I carry a Halfords brand tool bag (very good tbh!) containing this reduced kit:
Ratchet screwdriver + bits
Gas soldering iron kit, wire, multimeter
Spanners
Hammer
Screwdrivers
Pliers
Allen keys
Knife
plus the spider wrench in the spare wheel
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang