Basic tools

Water,

lug wrench (it amazes me how many people with trailers don't have a lug wrench that fits)

jack

Blanket to lay on road if changing tire (asphalt gets hot)

Tire plug kit

Code reader/reset tool. If you get a check engine light/reduced engine power this is really nice. It has saved me from tows multiple times. It has also let me help others.

Medical kit

That's just the things I seem to use.