Dont throw away your old Boarding Pass, it may contain personal information that could allow attackers to run targeted attacks on you! An attacker can send a spear phishing email to the victim reporting information on his flights. An attacker could also reset the PIN number associated with Star Alliance frequent flyer account, in the case of Cory, he tried to use the Forgot Pin reset and his friend question was, What is your Mothers maiden name?”]
Source: https://securityaffairs.co/wordpress/40807/digital-id/boarding-pass-personal-information.html