Whooo-ee! Hate to post following the Master, but-

raincheck- originally a ticket stub given when rain cancelled a game.
In stores now, it is a ticket or (recorded) promise given when some item, priced in a sale, is sold out but which guarantees the customer the item at the same price at a later date.

Brownie point- "a notional mark of achievment, or kudos for performing some creditable act."
Often credited to the Brownies, the lowest age group associated with the Girl Scouts (Guides in Canada and England(?)), but J. E. Lighter, Historical Dictionary of American Slang, found the oldest usage in Army jargon- "Blew his stack. Brownie points." 1944, MSU Folklore GF2.1.