Keep celery heads whole, wrap each of them separately in aluminum foil, and refrigerate. Plastic bags trap in the ethylene it produces, which hastens its demise. Aluminum foil allows the gas to escape, so your celery will stay fresh longer. 
Dip celery sticks into sauce, butter, yoghurt and also use them in salads and purees. Stuff peas, cheese or olives in chopped celery sticks and consume.