During my career in the USAF I was given many ammo cans, here is my favorite mod for the medium and large ammo cans; these are the ammo cans with the removable lids that close on each end.
What's in the can?
For this project you will need a medium or large ammo can, a drill, multiple sharp drill bits including a 1/2" bit, two 1/2" eye bolts each with a washer and two nuts, a sharpie or pencil, and some eye pro.
With the lid closed lightly mark the center of the center slot, eyeball it and darken your mark, adjusting it as needed.
Eye pro goes on here! Remove the lid and drill a small pilot hole on your mark, then a medium sized hole, and finally use your 1/2" bit; using three sizes of drill bits this way will make your work both easier and cleaner. Take your time, use oil if needed, I used Slip 2000 EWL.
For easier clean up I like to put a super magnet in a bag and clean up as I work, when I am done I turn the bag inside out and discard the bag and the filings.
Install the eye bolt, thread on the washer and one of the nuts, tighten the nut and then add and tighten the second nut. You could cut the unused portion of the bolt off if you wish; repeat for the remaining eye bolt.
Clean up any remaining metal shavings, add the lid and a couple locks and you are done!
Here are a few of my modified ammo cans, full of small arms ammo. A large can full of small arms ammo easily weighs 150 lbs; having all the cans tied together like that makes it more difficult to steal.
These modified ammo cans are also great for locking up tools in the back of your truck. If you have expensive first aid kits at work paint a can white with a red cross on it; stuff the fist aid kit into the can and instead of using a lock use a serially numbered plastic seal. Now instead of inventorying the entire first aid kit every few months you can just verify the serial number on the intact seal.