Keep it, it might come in useful. 留着它，也许会有用。
The money will come in handy when I want to travel. 我想去旅游时，这些钱会派上用场的。
Oh, that spanner will come in handy for fixing the plumbing.
Thanks for lending me your bike. It came in handy while my car was in the shop.
Those fabric scraps came in useful when I needed to mend the quilt.
See also: come in