three wifi flight passes for $6.50 each
Buy three (or more) flight pass codes for $6.50 each, and sell them for more to passengers on the flight.
I like little exercises like this (like when I hacked a Vegas cab line), because being a salesperson is uncomfortable. Creating value can be a scary, anxiety ridden process. You have to talk to people you don't know, who aren't expecting to talk to you, and often whose first reaction isn't welcoming. You have to overcome all these obstacles and get them to see the value you're bringing.
That's why while making $20 off a couple of passes isn't a material amount of money, it's very material in the skills you need to use and hone to sell other, more expensive services or goods.