Depending on what developer you are using, its probably gonna die in about a day or two. The stop bath should be good, although its smelly and it may actually get stronger if it dehydrates. Your fixer may not be as good either in a few'll probably turn yellow. So basically, your best bet is to find some containers to store your chemicals in. Most anything that is air tight will do...used jars, bottles, etc. No need to really spend $10 on a container thats 'designated' for photo use. The tin foil covered trays really just let too much air in, not to mention the exposed surface area is much greater in the tray. The only developer that I know of which would probably be fine for a few weeks in an open uncovered tray is Anso 130. If there was a nuclear fallout then the only things that would still be active are roaches and Ansco 130.