Lose my shit, that's what I'd do. But if I could get my head on straight, I'd slam on the brakes and pull a U-Turn as fast as I could. Loljk, I suck at U-turns.
WWYD if you were alone at an airport in a foreign country, and while your back was turned somebody made off with all your luggage, including your phone, passport, ID, money, boarding pass, and everything else?