One of the most useful materials to the scratch builder or converter is plasticard. The kind made from the same type of plastic as the models themselves. I've stumbled across a free alternative, so I thought I would share.
My family consume a fair amount of ice-cream and the vac-formed tubs that they are sold in are a great free poly compatible substitute. The cheaper the ice-cream the thinner the material.
The white hull panels on this model are all made from vac-formed tubs, I'll never buy plasticard again, although I may buy slightly more expensive ice-cream if I need card slightly thicker.