I have a rule for myself that I won't check bags, so I always travel with a carry-on suitcase and a backpack. After much trial and error I've developed a pretty solid packing list for my backpack AKA "personal item."
My new go-to backpack is from KAKA (pictured above). I have this particular backpack in large and it's the perfect amount of space. Added bonus- it's waterproof!
Hand Lotion (travel size)
Face Oil or Face Mist (travel size)
Toothbrush and toothpaste
Hand sanitizer
Tissues (travel size)
Umbrella (in outside pocket with metal key clip- see below)
Hat
Passport
Phone Charger
Portable Power Bank like this one from Anker. I usually travel with 2 just to be safe.
Tablet & charger (or laptop if desired).
Puzzlebook- yes they still exist and can help save the battery life on your electronic devices. They may also help you fall asleep ;)
Two Pens- black or blue only.
Copy of hotel/flight/transportation reservations (and screen shots on your phone)
Camera
Reusable water bottle, like this 21oz one by Hydro Flask (in outside pocket with metal key clip- see below)
Two Metal Key Clips (Carabiner Hooks). I avoid the screw fasten ones since it takes longer to open and close. I'm using a green one in the picture above for my water bottle.
Selfie stick. All jokes aside, when you travel alone this can come in handy!
Earplugs
Eye mask. This one by Bedtime Bliss is cheap and contours around your eyes.
Neck pillow. I have tried just about all of them and the J-pillow is my favorite.
Hair tie
Prescription medications and doctor's notes. I've never been asked for the doctor's notes, but I don't want to risk it and have them confiscated. Better safe than sorry!
Small cross-body purse or similar item. I keep money, passports and other important items in a small purse. When it's time to fly I just toss the purse in the backpack so that I'm not over the limit of allowed personal items.
*I do not have any affiliations with any of the companies I supply links to and do not make any profit if you decide to order from them.