Here are some old Rogue Trader plastic marines (from the original Imperial Marines box) done over with alterations. I did these years ago, these are relics from the early nineties, but I'm still quite proud of how inventive these alterations are (mostly with weaponry). The execution is so immediate: not concerned too much with quality so much as being legible.
Here's a scratchbuilt AK-47, with strap, I can see the banana-clip is made from bolter magazines, aside from that I can't tell what the rest is made of.
Bolter with strap (paper cut into strip and painted) with wire tail-stock. I can see that this arm took a little persuasion to get into more forcible pose.
Uzi, all scratchbuilt. Textured handgrip is a piece of Sculpey that I rolled a gnurled X-Acto handle grip on to get the patterned texture.
Battle-Damage. Cut and melted away plastic pack, a soldering iron or glue-gun tip was probably involved, and the 'exposed' metal part came from a little box of cool watch parts I got from a craft store.
Two magazine duct-taped together. Note the painted on 'eyes' on the nose cone. I think I did some WWII style teeth as well on some of the cones-faces.
Then there's this guy: Skeletal robot tripod, from some Citadel skeleton parts, an Eldar arm and a chopped up chaos autocannon.