Leftover part of a ticket

STUB

["\"What you might hold onto after entering a concert?\""]

The clue "Leftover part of a ticket" leads to the answer "STUB" through a straightforward definition. When you use a ticket for an event, the portion that is typically torn off and retained by the ticket holder is called a stub. This is the part of the ticket that is left over after the main portion is taken by the ticket collector. Therefore, the word "stub" fits the description of being the leftover part of a ticket.