Here are some C's.

Cardboard: The magical insulation stuff. You should always have something between you and the ground when you bed down at night, and cardboard is warm, radiates heat, though on it's own it is not enough, even in summer. If you have no blankets then wrapping yourself in cardboard does help, but it is hard to keep in place. Cardboard is free and plentiful in town centres at night, outside shops, in bins, in cardboard recycling areas. It is alo good to sit on if you are begging or waiting for a soup run.

Cardboard is returnable to it's bins if you don't want to leave it as a telltale to where you are sleeping, and it is easily replaced, keep it dry, wet cardboard is horrible and useless.
The best cardboard is big thick boxes from furniture or Electrical equipment, luxury this deep cardboard. I used to sleep behind a massive cardboard bank where people disposed of such boxes. :)

If you can only find one small bit of cardboard, put it under your back, not your legs.

Carpet cuttings: strips of cardboard and old mats are an alternative to cardboard, comfortable but not as warm as cardboard, and they can contain dust and mites that make you sneeze and cough, they can be bitty and falling apart and once they get damp they are no good.