rain check
noun
• a ticket given for later use when a sporting fixture or other outdoor event is interrupted or postponed by rain.
• a coupon issued to a customer by a shop, guaranteeing that a sale item which is out of stock may be purchased by that customer at a later date at the same reduced price.
take a rain check
• politely decline an offer, with the implication that one may take it up at a later date.
• "they wanted me to come along for the ride but I took a rain check"
