Over packing can be a real pain in the ass on vacations and definitely slow you down.
Important things to consider are:
-Do you have multiple layovers?
-Will you be using public transportation or renting a car?
-Can you carry all your luggage while looking at your phone/a map?
On international flights you get a free checked bag (at least on all the airlines I’m aware of), so I typically say take advantage of that! That does not mean pack more crap, it means check your bag, whatever size, so you don’t have to carry it through the airport, ESPECIALLY if you have multiple layovers. Check a small duffle, and then bring a backpack or small rolling suitcase as your carry on. This will allow you to carry both bags and have a free hand. I have been standing in Paris, in the rain with a big rolling bag, and a small rolling bag and no way to look at my GPS without stopping in the rain- this sucks.
For your carry on, pack the important things like your camera, chargers, a change of clothes, makeup, things that are horribly annoying to replace. For your person item (which I think it more essential to pack properly), pack everything you want to have access to during your long flights. I haaate people that are constantly up in the overhead bins pulling down their luggage rummaging through their belongings in the aisle- don’t be that person. My personal item is typically a large purse/tote or small backpack that I can shove under the seat in front of me. This should contain your phone, passport, travel accommodations, directions (always have a printed copy in case your phone dies or chooses to act up in a foreign country), phone charger, any entertainment (i.e. tablet, book, magazines), aspirin/ibuprofen (trust me, when you need it on a 12 hour flight, you don’t want to be without), tums/gas-x (gas expands when you are flying, and it can give you the worst cramps!), hand lotion, lip balm, tooth brush & paste (seriously), earbuds/headphones, snacks, refillable water bottle, and I always pack a blanket even though you usually get one on long flights.
Always make sure your bags aren’t packed to the brim so you have room to bring back things you found abroad! If you are short on space upon return, one trick is to wear your bulkier items/ carry your coat.