Yes, you can still buy a plane ticket at the airport on the day of travel, but the process has changed significantly from the "walk-up" era of the past. Most major airlines maintain ticket counters in the departures hall where agents can sell you a seat if one is available. However, "last-minute" airport tickets are almost always the most expensive way to fly. Since you are booking a "full-fare" ticket without the benefit of advance-purchase discounts, the price can be three to four times higher than a ticket bought weeks earlier. Furthermore, for security reasons, some airlines may flag "cash" walk-up purchases for extra screening (SSS on your boarding pass). Many modern travelers find that it is actually faster and cheaper to use their smartphone to book a ticket via the airline's app while standing in the terminal, as it allows them to compare prices across different times or nearby airports. If you are trying to catch a flight departing in less than an hour, most airlines will stop selling tickets because of the time required to process baggage and clear security, so "last minute" usually means at least 90 minutes to two hours before departure.