mountain money
v. phr.— «If you want to go camping or hiking in the desert one of the first skills you learn is how to frost a rock, especially if you’ve forgotten to pack any “mountain money.”» —“Re: Glue?” by John M. Williams bit.listserv.words-l Jan. 1, 1996. (source: Double-Tongued Dictionary)
Further reading
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...