You know the sort of thing - left over breakfast sausages become dinner time stew. Old 1" Very pistol cartridge cases (showing me age here!) making a useful waterproof fag case. Using the rubber 'O' rings from 81mm mortar containers as 'trouser blousers'. Taking the turret of a CVR(W) Fox sticking it on a CVT(R) chassis to make a Sabre. Using those opaque plastic inserts from ammo boxes as a handy chinagraph notepad. Using the old round L2 grenade tin with the spring loaded lid clip as a pressure cooker for the section's tinned compo. Filling the old blue plastic salt container from the 10 man pack with rifle oil for the GPMG. Any others spring to mind?