Only carry two tools.
A hammer and a big hammer.

I can fix most stuff with a hammer but, if that don't work I go at it with a big hammer.

 

So now we know whose toolbox to break into so we can buy more beer.

x2 on what tumba said. As long as gasket is in good condition and your not in a high humidity area you should be alright. I am running a 27" weatherguard. It has a few dewalt cordless things. LOTS of wrenches. A 24" and 36" Ridgid Pipe wrench. Oil absorbant diapers. I have a 20lb fire extinguisher bracket attached to a piece of angle aluminum that braces is against the bottom of the toolbox and bed. (No holes in toolbox).

I also have an igloo 1ce cube rated at 55 cans.

 

cordless drill, bits, tools, rags, recovery strap, tie downs, and spot light...

in the winter, when i got it, it had a leak, and snow would get inside...
i added some weather stripping, and now its sealed tight, no water even after using the car wash...

 

Buncha crap really. 3 gallons of 2 stroke oil, random tools, extra belt, oil, ATF, chains, straps, etc. I need to clean it out bad...

 

Used to keep a hydraulic jack in there, until it leaked some oil out. Never did/will get it all cleaned out no matter how much I try with brake cleaner and paper towels.

Right now I keep some motor oil, a baseball bat (don't ask) and some chains. And a tool box with some sockets and odd parts.

 

I keep Dewalt cordless drill, recipricating saw, flashlight, battery charger and batteries, a skill saw, lots of hand tools and a screw box in my tool box. I haven't had any problems with rust unless I leave the top opened, get busy and forget to close it if it rains.

 

I've got a Craftsmen 300+ piece toolbox, various electrical equipment from light sockets, breakers, conduit, etc, a Craftsmen toolbox full of various small circuit board equipment, like soldering stuff, dremels, and some smaller items. Then I've got my plastic boxes full of screws, nuts, bolts, wood screws, machine screws, springs, etc. Along with plastic boxes full of various weight hammers, sledges, crowbars, etc. Along with some other stuff, like my Dewalt Cordless hammer drill, power drill, flashlight, circular saw, and sawzall. Then I got the random stuff like fuses for the truck, tow straps, chains, tiedowns, twine/rope, caution flags, two different size hitches with different size *****, paper towels, toilet paper, blow torch, hand wood saw, small 3 ton floor jack, torque wrench with sae and metric sockets... and like a few other doo dads...

 

Just in case an emergency baseball game happens to break out

Ok lets see, all my Klein electrician tools, a whole bunch of sockets and ratchets, random pliers and vice-grips and what not, tow straps, tow chains, spanner wrench for hydrants, Mechanix gloves, three or four Maglights, milk crate with blankets, rags, hi-vis jacket, and other random cloth things, jumper cables, cordless drill, BFH (big ****ing hammer), ice scraper (christmas gift. I live in Houston?), WD-40, PB blaster, Royal Purple 10W-30, four way, and of course the good ole' emergency baseball bat