Upgrade the tow strap to a snatch strap. A snatch strap will make recoveries easier and less damage prone. Snatch straps stretch while tow straps don't. You'll want this kind of stretch in a recovery. They are more expensive but well worth it IMHO.

Basic mechanic set with socket, open/closed end wrenches, screw drivers.

Oil: 6 qt.
Tranny: 1 qt.
Brake: 1 sm bottle
Coolant: 1 gal
Gas: 5 gal. Use a NATO can or a scepter can. Both are good quality and don't leak fumes. Blitz style Jerry cans with a screw on metal cap are not so leak free.
Canvas tarp: I use an old marine corp nylon blanket. Great to cover the ground when you have to lay in it. Also good to put dirty broken parts in after a trail breakdown or as a blanket should you forget your sleeping bag (like on a "3 hr tour" trip) or if its not be warm enough.

ABC fire Extinguisher: This should either be securely mounted or stored because in an accident they will become a heavy projectile.

Water: 5 gal (recommend a dedicated container like the military scepter made for water) but any setup works really.
Energy Bars: 1 box.
Camping gear.

There's probably more. I keep a lot of these things in my rig like the basic tools and extinguisher. The rest I keep in a box ready to go on my next outing.