A long time ago, a few airlines only sold tickets on a "standby" basis (mainly Europe); you showed up, waited on line...They issued an "intent to fly" document, which the pp office accepted for getting a pp on short (same day) notice. In lieu of purchasing refundable tickets (and then cancelling), do any airlines issue an "itf" document?
I haven't seen one or known anyone to encounter one of those in the US or Europe, in well over 15 years. I have seen lots of self-printed, confirmed flight bookings "on hold" used -- which means they weren't ticketed at the time of use for these purposes.