I'm a pack rack, and I put that big bed to good use.
I take a big duffle bag in the bed. In that bag is a designated tool bag...or "break bag", as I call it. Ironic, since this thing never breaks, but...
Tool bag:
Sockets and wrenches of the appropriate size -(8mm, 10, 12, 14, and 17). Make sure the 17 fits in the alloy wheels, if you have them.
Small pipe wrench
Mid size slip joint pliers
A lot of tire plugs and appropriate tool.
A small can of fix-a-flat.
Mechanics wire
Regular wire and some butt connectors
Zip ties
A few hose clamps of various sizes
A few common bolts/nuts
Shoe Goo
Electric and duct tape
1 quart of oil (in ziplock if open)
Known good used plug (in box to prevent damage)
A aftermarket plug cap from a previous repair on my 1st 700.
A small Slime brand compressor.
I'm planning to add a small test light soon.
Inside the duffle bag with the "break bag":
A yank strap/hitch pin
At least one ratchet strap
Bungee cords
*Long sleeve shirt
*Rain poncho
*My lightweight jacket when not in use
*Disposable gloves (makes riding gloves much warmer in a pinch)
Lighter
Food/snacks that don't need ice
A sterno stove and fuel
The rocker switch for my winch (I only have the remote connector permanently installed)
A small shovel/axe/saw kit from amazon
*--when weather conditions dictate them necessary.
I also carry a passenger bag (I'm solo 99% of the time) with:
My asshole/predator repellant
Whatever I'm drinking in a thermos
Ibuprofen
Sun block
Goggles
Toilet paper
Eyeglass wipes
Stand alone deactivated phone with GPS/map app
Go Pro and mounts (rarely used these days)
Phone chargers and charge pack.
SPOT personal satellite tracker
I also carry a 4 gallon Koplin fuel Pak, but only put 2 gallons in it.
And...a cooler. With a big bottle of whiskey, sodas, and water. And food that needs to be cold. And a gallon of sunny delight.
Occasionally, a folding chair.
I'm sure I'm forgetting something...
This sounds like a lot more than it is. Honestly, the passenger bag could be combined with the duffle, but I like having it at hand.