Any kind of cardboard? What about plastic bottles? Should they be flattened, or no matter?

Denise is correct... Plastic and cans need to be sorted, and they could be flattened if you want to save space (but not required). Regarding cardboard, we can take BALED cardboard, or loose, flattened boxes up to 100 lbs.

Not sure about the cardboard but plastic bottles or cans do not need to be flattened but you do you need to separate them either before or at the center