The Truck Tool Box has come a long ways in 50 years. What used to roll around the bed of the truck now rests comfortably out of the way across the bed. The cross-over tool box being the most common, it stretches across the bed of the truck, resting on the bed rails on either side. Positioned up behind the cab and up off the bed floor, it is not only handy but provides maximum carrying room in the bed. The tools and stuff in the box are easy to get at. And so is what you're hauling!
You can find these truck tool boxes made out of aluminum, steel, and heavy duty poly plastics. The steel ones, while probably the most sturdy, are also the most heavy. Aluminum is now quite sturdy and much lighter weight. This is important if you are hauling a lot of heavy gear or equipment. They also don't rust. The hard plastic boxes are lighter weight as well, but not as sturdy I don't think.
There are also several options for the lids providing access to the tools in the box. The single lid is okay, but you pretty much need to be in the bed of the truck to make that work. The upside is that you can see ALL of the contents, and access any longer tools easier. There are also dual lids, gull wing lids, and split lids - which open independently and are more accessible from the side of the truck.
The lighter weight aluminum tool boxes are also handy if you have need for a portable box, to haul around a job site, or to put in the back of your Van, SUV, or old station wagon. As they are lighter weight and sturdy, they are much easier to lug in and out, or around.
They are making hand held tool boxes now that are made to fit specific places in your rig. This gives you the light weight mobility of an aluminum hand-held box, with the convenience of a stationery made-to-fit box which won't be rolling around your truck or van. There are cross-over models, as well as models that fit in the wheel wells or behind or under the seats.
Of course there are still the regular size hand held aluminum tool boxes that are made to be carried around to whereever you're working, whether it's your job or your weekend project. Made of aluminum makes them light weight, and so easier to carry and easier to store.