Along with two bags full of clothes, toiletries, and gifts, I carry a good sized carry-on bag on my overseas flights. This bag has lots of space, pockets and zippers galore and room for everything I need for my long flight.
I keep my passport and plane ticket in an outer pocket ready for easy access. I also keep my oversized wallet handy but in a different compartment. I know where these three items are at all times - I could lose everything else and still survive with these essentials.
I have my laptop and power cable in another compartment and use it while waiting for my flight. A book and a magazine are in the bag and will not be needed until I am in the air. I also bring a bag of trail mix in case the airline food isn't up to par.
Smaller items are in a little pocket of my backpack. These include gum, mints, pens, keys, change, and any other little things I need to stow. I keep my noise reduction headphones near the top of my bag since they will be one of the first items out as soon as I get my seat. My glasses are also on top because I will need them for reading.
I have space for a small half inch binder that I put various documents in. I usually have a local map or two, computer print outs of places I want to visit, and a small list of translated words and phrases. A copy of my itinerary is also in the binder. My checklist is also in here.
I also stash anything that is breakable in my backpack. I wrap up these fragile items in layers of tissue and place them so they don't get jostled around. I try not to carry anything that can be broken with me but sometimes it is inevitable.
It is a good idea to pack one change of clothes just in case your bags don't arrive at the same time as you do. This can just be a T-shirt, pair of shorts and shower slippers. This will hold you until you can file your claim and go shopping.
I try to leave enough room for some duty free goodies. I am a smoker and take advantage of the tax free cigarettes. I take a risk buying three or six cartons depending on the length of my trip. The risk is that most countries only allow you to bring in one carton. I still haven't figured out this rule since most duty free shops sell the cigarette cartons in 2 or 3 packs or have a buy one get one special. I have never been stopped by the customs officers but I do keep the duty free bag out of site in my backpack.
I avoid carrying liquids because of the hassle of going through security. If allowed, I do carry a bottle of water with me. I like to keep hydrated on the flight. Some airports will let you bring it on board and others won't.
Your other essentials may be some sort of music device like an I-Pod or your cell phone. I have an unlocked, tri-band phone that I can use in Thailand just by adding a SIM card. That is also placed in an easy to access part of the bag so that I can use it upon arrival.
Packing the essentials in your carry-on bag will make your flight go a little easier. Plan for your bags being lost and that will help determine what you need to carry on board. Hopefully, your bags are waiting for you, but just in case, you don't want your vacation completely spoiled. So, pack your carry-on bag with the necessities and enjoy your flight.