Last year I lost my wallet at airport (first time in 10+ years travel) before I was to go through security. Even though I retraced my steps at airport, couldn't find my wallet and had to board plane to make my flight.

Although UA check-in counter gave me boarding pass after I answered couple of MP account-specific questions, I had to run the TSA gauntlet of ID authentication (30-min. process of getting a TSA-specialized supervisor to pull up my records, and asking me specific questions on where I lived and worked dating back almost 10 years), w/o any actual ID cards on me. After I successfully got through security, while walking toward my gate, heard PA broadcast my name to claim stuff from Lost & Found. So I got my wallet back with all contents, and all was good plus I survived TSA authentication.