Household items for plants to stand on?

So I'm trying to figure out what I can use to support my plants while avoiding spending money. What type of things do you guys use?

I have a lot of cardboard boxes lying around but obviously they seem like a fire hazard. I've been looking through the free section on craigslist but what type of things should I be looking for? Are plastics ok?

books, theyre perfect, you can set height easily..

Scrap 2x4s cut to 1' long stack em up like legos. I use cheap lil rubbermaid stools they are like 10" square and about a 10" tall.

PVC table is a bad ass idea, and then a sheet of wood on top. I flip pots upside down, if neccesary, but moving the lights has been better for me.