Terragenisis used to have loads of 6mm projects, using blister packs and the like. However, it looks like the site is completely and totally gone

(as in, site suspended, domain available to buy) You could see if the wayback machine has any archives of it, or if it got moved somewhere. I spent many an hour marvelling at the stuff people did with bits of leftover junk

I have seen buildings made from blister packs, with granny grating for windows. Blister packs (you may be detecting a them) for batteries can be used for huts or the roof of a factory.
Craft stores and places like The Works are great for beads and stuff.
One of the train scales "Z", is 1:220, so barrels and crates should be okay in 1:300 (if you squint).
cp models has some 6mm scenery that is worth a look for inspiration, as I think does Brigade Models and probably Irregular Mins