The number one thing you’re likely to overpack is clothes. Fact is, you never need the amount of clothes you think you need.
Never, ever, ever.
The best way to restrict yourself to bringing only the absolute necessities is to divide your suitcase into quadrants.
Quadrants 1 and 2 (e.g., the left half) are reserved for clothes. Any time you find yourself adding clothes to the third or fourth quadrants, you’re veering into overpacking territory and need to edit your travel wardrobe.
Quandrant 3 can be reserved for shoes, socks, a travel umbrella, etc. Any time your shoe quota starts veering into the fourth quadrant, you’re overpacking.
Quandrant 4 can be reserved for hygiene and hair care products, as well as electronics, power cords, plug adapters and the like.
Finally, if you have a suitcase that has an expansion zipper, and if you feel the need to use it for your departure flight, then you, my friend, are overpacking.
The only time you should expand your suitcase is midway through your trip or for your return flight home.