I spent time on a LOT of airplanes this summer. I flew from Portland to DC. From DC to Boston. From Boston to Portland. From Portland to Toronto. Etc. Etc. Etc.
Here is my final, curated list of what I put in my carry-on bag. This will differ for everyone, but I encourage you to think carefully about every item - life on the plane is so much better when you have a lightweight bag and you don't have to spend time scrabbling around in it to find what you want.
1. Electronics: for me this means a laptop, an iPad and a phone. Which seems like a lot, but I don't feel comfortable putting my laptop in checked luggage. I'd ditch it if possible. Headphones or earbuds to go with these.
2. A book. Ok, usually two books, since I am invariably right near the end of one when it's time to fly.
3. SNACKS. Need I say more?
4. Glasses. I use an impossible combination of eyeglasses each day. To travel, I wear my "regular" glasses and pack my close-in bifocals, for screens and books. Don't ask; if this is not your reality then thank your lucky stars.
5. Wallet, chapstick, inhaler, any jewelry I'd hate to lose, and prescriptions.
That's it. I've pretty much given up bringing my own water bottle, because it's too big for the space I have and always ends up rolling around on the floor. I do feel badly about the plastic cups I'm using on the plane, so perhaps there is a small water bottle in my future.
Now, I'm not suggesting that your packing list should be the same as mine, but do yourself a favor and think about what you want and need to have with you. Put the rest in checked luggage. Or, if you hate to check anything, at least put the rest in a bag that will spend the flight in the overhead, not at your feet.