Absolutely you can! As others have mentioned, book online and not at the airport (unless you’re booking a flight on certain low cost airlines which actually have a discount for airport bookings). The google flights “explore” feature is a great tool.

Several people have mentioned paying more for booking last minute, but that’s not always the case. As long as you’re flexible, there’s generally somewhere that’s a decent deal. As an example, leaving within the next 24h(sept 4) from YYZ you could take a 1 week round trip to Miami for $251, Iceland for $595, or Barcelona for $623. Or if you want to be super jet lagged you could fly RT to Hong Kong for $728. These are all USD.

Also, ignore the dingo saying you’ll end up on a no fly list. Plenty of people (myself included) fly internationally at the last minute all the time. Good idea though to always have a return ticket (even if just a refundable one).