How to keep my crickets alive longer?

I just recently (today) purchased about 48 large crickets(petsmart description), came home put them in a "bug box" that's about 11' long, 4' wide, and 4' tall. In the "bug box" I put egg crate, a gatorade lid of water, and a piece of fresh celery and they are dying already. What am I doing wrong? What should I do differently and should I leave them in the bag from petsmart? I need these things to last at least a week or two cause I don't want to have to keep making trips to petsmart. Also, these are for my geckos. Thanks for the help.