1. To exchange one's chips (small discs used to represent money in some betting games, like poker) for money when one is done playing a game. I think I'm going to quit while I'm ahead and cash in my chips.

2. By extension, to stop participating in any gathering or activity. Well, it's been fun, fellas, but it's time for me to cash in my chips.

3. To leave a gathering and/or go to bed. I have to be up early tomorrow, so I'm going to cash in my chips.

4. To die. We were so lucky to avoid that massive accident—we could have cashed in our chips!