Who else routinely uses 1-2 ribs of celery, then, a week later, opens the fridge to find a sad, floppy bunch destined for the compost pile? My solution: mirepoix. Mirepoix is the French term for the finely chopped onion-carrot-celery mixture that forms the base of many soups and sauces. Chances are you've got some carrots and onions sitting around. With a food processor, a few freezer containers and five minutes, you can use up your bunch of celery and have a few batches of mirepoix ready for the next time you need it.
The traditional ratio is 2:1:1; two parts onion, 1 part celery, one part carrot, but I improvise based on what I have on hand. Generally that works out to an onion (peeled) + 1 good-sized carrot (peeled or scrubbed) or a handful of baby carrots + 1 rib of celery (peeled). I use my food processor to roughly chop the carrot, then add the onion and celery (which chop more quickly), give a few pulses, and I'm done.
I store the mirepoix in containers in the freezer where it waits until the next time I make a soup, sauce, or stew. With the bulk of the chopping work already done, I can throw together a decent meal in no time.
If you want to keep your celery crisp for snacks (celery and peanut butter! celery and cream cheese! celery and a string cheese!), a Cuisipro Herb Keeper does a good job. This tall, clear plastic container keeps a small amount of water in the bottom and seals at the top to keep moisture locked in. Good for bunches of cilantro or parsley, too. If your kids are older and breakage isn't as much of an issue, just store your celery in the fridge in a tall, stable glass vase sealed with plastic wrap.