My .02 Lupins:
For baggage (tent bags, tarps, bedrolls, etc.) I'd suggest GS or sculpy. You could also use tissue paper or similar, soaked in white glue water mix as dust covers/tarp.
For the sculpy, rough fit on the vehicle before baking... use a fine mesh med gauze to give texture and obscure any fingerprints.
Lots of O scale accessories out there that would work.
Check out 1/35 armor modeling sites for ideas on stowage techniques and tips.
Pacarat