Question

a rain check (on something)
1. a piece of paper allowing one to see an event—which has been canceled—at a later time. (Originally said of sporting events that had to be canceled because of rain. *Typically: get ~; have ~; take ~; give someone ~.)
  The game was canceled because of the storm, but we all got rain checks on it.
  I can't use a rain check because I'm leaving town for a month.
2. a reissuance of an invitation at a later date. (Said to someone who has invited you to something that you cannot attend now, but would like to attend at a later time. *Typically: get ~; have ~; take ~; give someone ~.)
  We would love to come to your house, but we are busy next Saturday. Could we take a rain check on your kind invitation?
  Oh, yes. You have a rain check that's good anytime you can come by and visit.
3. a piece of paper that allows one to purchase an item on sale at a later date. (Stores issue these pieces of paper when they run out of specially priced sale merchandise. *Typically: get ~; have ~; take ~; give someone ~.)
  The store was all out of the shampoo they advertised, but I got a rain check.
  Yes, you should always take a rain check so you can get it at the sale price later when they have more.