I am a notorious overpacker. This past fall I went to Gatlinberg, TN for 2 days and actually packed probably 5 outfits. It's ridiculous. However, I really do know how to pack the airplane carry-on, which requires much less important decisions.
First off, the bag. I prefer large totes (from Longchamp, Tory Burch, Kate Spade, or Lilly Pulitzer). It helps if they zip at the top so you don't have to worry about things getting lost. Second, I like to pack the big items first so I can figure out how pack around them. My laptop (and charger! Don't forget chargers!) and camera (if I'm not bringing its huge case) are the two big tech items I'll bring, as well as my phone and headphones. I always bring my makeup bag in my carry on, because you never know if you are going to lose your suitcase! Same thing goes with jewelry. I don't really wear much jewelry on a daily basis, and I'll probably be wearing my usual rings/bracelets on the flight anyway. But, it's always better to keep your jewelry with you in a cute bag.
I cannot forget to bring my passport for Mexico this weekend. That would be counterproductive! Also bring your wallet with the appropriate cash/cards, and put it in a side pocket of the bag. Other little items I keep in the side pocket are Visine (my eyes get red easily) and lip balm. Lastly, I like to keep a water bottle in my bag so I can fill it up when I get to the airport.
What do y'all pack in your carry on? Leave tips and ideas in the comments below!