Bring a water bottle with your carry-on luggage. Make sure your bottle is empty when going through customs and place it in a separate bin for the X-ray machine. Contrary to popular belief, you can take a water bottle on most airlines. When you are in the holding area, fill it up at the tap, and save yourself from buying that $3.00 bottle of water.
Pack your lunch. You will most likely pack a better meal than an airport slippery meat and processed cheese sandwich and for a quarter of the cost. Be careful about bringing nuts, fruit, and meat. Check the regulations of your country of entry before taking it through customs. I personally have never had an issue.
Measure and weigh your bags before you arrive. If your carry-on baggage doesn’t meet requirements, the price for additional baggage is higher the day of your flight. It is cheaper to add an additional bag online a few days before your flight than the day of your flight. I personally travel with a soft sided duffle. It can be pushed and squished into the measuring box even if I may have overloaded it a bit.