It is never good idea to leave food in an open can. Once a can is opened, it begins to oxidise, and you risk food poisoning. It is best to remove any unused food, and store in a non-metal container.
With proper care your pan should be non-stick, assuming it is cast iron. It just needs to be 'seasoned' properly. To do this, coat your pan with a THIN coating of vegetable oil, place upside down on a piece of aluminium foil (to catch drips) in a moderate oven for 30-60 minutes. Cool to room...