What constitutes a valid e-ticket?

[NM]

I carry my PDA/phone which has all of my calendar events. In the calendar event I detail the flight number, departure/arrival and booking reference and ticket type = eticket.

Probably a god idea to include the e-ticket number as well, just for reference. I keep the airline's record locator (booking reference) code as well as the ticket number in my PPC trip planner.