Pennsylvania? Probably not the same things you could in Alabama
But, I'll throw in with Sandy about the greens (lettuce, spinach, kale, mustard,...or a mix of all these) and radish...all are fast growing. I have no idea what your weather is right now, though...greens might be better when it's a bit cooler, maybe? Green beans might be an option, too. These are all from seed.
How big is the "tin barrel thing"...especially the depth? Has it got drainage holes in it?
It looks like your first possible frost is around the first of October so you've got a good 60 days to work with. You could even extend that time frame with with a little protection (simple sheet thrown over the barrel thing) or a more elaborate plastic tent.
Do a little research and see what will produce in the next 60 days (you maybe have a *very* short harvest period for some vegetables) and possibly visit some local nurseries and get some transplants to work with...??? That would shave off six weeks of grow time for some vegetables.
With the crazy weather that we've been having your season may last well beyond the 60 days or end well before it. Cool weather crops will extend better into the cooler weather.
Just some brain-damaged thoughts.
Best wishes.