In the tool department at the local Borg home improvement center I found a plastic stepstool with folding handle that has a lockable storage compartment under the lid. Originally it was meant for some sort of portable toolbox/step stool. The stool is very lightweight, the handle makes it easy to carry, it is just right for sitting on for low shots and standing on for high and the thing cost under $4 USD. I transport 5x7 film holders, light meters, filters, front-mounted packard shutters, rags, cable releases and filters in it out in the field. It really comes in handy for just taking a break as well. You could also adapt a shoulder carrying strap to it very easily if you wanted.
I found it in a shop named Menards in Michigan, but places like Home Depot, Builders Square, and Lowes as well as a good hardware store probably have similar items. I liked it so much I returned and bought one for the studio and the workshop as well.
Joe