I just received my American Airlines eSummary and one of the highlights mentioned is that Admirals Club lounges will be going cashless as of October 1, 2015.
“Beginning October 1, we will only accept credit and debit cards as a form of payment inside our lounges. Cash will no longer be accepted. This includes payment for items like:
The change will align our lounge and onboard payment options, and will allow us to serve you better.”
Tips, of course, may still be left in cash form.