The money, or spare that you know has fallen in, and is in the couch that you leave there until one day when you're totally broke you dig through the couch, thus "cashing out" your couch reserves.
Person one: I can't go tonight i'm totally broke...
Person two: How long since you've called on your couch reserves?
Person one: It's been awhile, hold on...
Person one: Yeah, I can go!!! I found $15.67 in my couch reserves!!!