I recently put together a toolbox for my truck. I have has bags and boxes in the past, but I wasn't happy with them. I finally found exactly what I wanted at sears 2 months ago. Its a craftsman professional series carpenter/plumber tool tote, 18"X8"X7" (approx). It has a ton of pockets of varying sizes inside and out, loops for pliers/ratchets, straps with velcro, pencil holders even a metal clip to hang your tape measure! It is awesome!
As for whats in it, I have a lot.
-small ball peen hammer,
-24 piece 1/4'' SOCKET SET,
-tool pouch with asst. screwdrivers, needlenose pliers, reg pliers, cicuit tester, couple -comb. wrenches.
in the tote,
-*3/8'' socket wrench with, 1/2", 9/16", (all the bolts on my snowblowers are either or) -mixed deep sockets,
-spark plug sockets,
-12 piece nut driver set,
-12 piece comb. wrench set (met. and sae) in a roll,
-compartment box of nuts, bolts, washers.
-19.2v craftsman impact wrench (awesome!)
-leather nail pouch on the tape measure holder (tape measure in it.)
-box of phillips head bits,
-*snow blower shear pins,
I think thats about it. a lot of that stuff you wont need for the trail. I use most of that stuff a lot though
Also under the seat is,
-first aid kit,
-swiss army knife,
-clevis hitch and shackle,
-black and decker charger/compressor/ac generator
in the truck i always have
a fire extinguisher is prob a goo idea too.
This is a huge list and most of it you might never use. I fit all this stuff and I can assure you the tuck isn't cluttered, its very organized. If ur in so-cal u prob wont need *snow blower shear pins and a wool hat. I like to be ready and help others if I had to. Make your tool kit, box, tote to fit your needs. Sorry I got a little over the top with this one!