Layer feed is made to most effectively produce eggs. In a pinch, I wouldn't worry about trying to formulate something to get them to lay.
If you can get back to the feed store in a day or two, just concentrate on keeping their tummies full. They might not lay as well for a few days afterwards, but it shouldn't affect their overall health.
They can eat anything we consider cereal, rice or grains. Oatmeal, bread, wild birdseed, breakfast cereals, cooked noodles, etc. Canned or fresh veggies you might have on hand, tuna, etc. pretty much anything you eat. I'm lactose intolerant myself so I really don't eat anything that they can't digest. They like pretty much any other animal's food - I think mine might kill the dog for canned dog food, also horse food, rabbit food, etc. I get them leftover food from work all the time - it's kinda nice that they can eat almost anything.
The benefit is that you can usually get wild bird seed and rabbit pellets at places like
WalMart that are open more hours than your feed store. Just give them some of that and some kind of veggies for variety, and buy some real chicken food the next chance you get. That's what I'd do.