Despite it already being (arguably) the most useful tool I have for building, I think it's time to modify my pickup to allow for a greater variety of loads. My solution is to add a lumber rack, and a flat deck on top of the bed. There will be a permanent "U" of wood around the edge of the bed that is bolted into the metal (as shown below):
The rack will bolt into the "U" when needed, and will allow me to carry really long items (lumber, rebar, roundwood, PVC, etc...):
The deck will allow me to carry large, flat things without the wheel wells getting in the way (such as 4X8 sheets of anything). The deck will be made up of 3 light-enough-for-one-person-to-maneuver panels that slide on, and lock in place.
The space underneath the deck can be used to transport tools. The idea is that eventually I will put a locking mechanism on the tailgate, and then I can store tools in rubbermaid containers (safe from rain and/or theft) in this space.
The whole setup should be really useful, and can be taken off if ever I need to transport a load of dirt, sand, gravel, etc...
In the next couple days, there should be photos for viewing, if all goes well.