Note: I would like to qualify this list with the disclaimer that I don't take all of these items on every flight. However, that would be mostly untrue. Any flight over about 4 hours, and my bag is stuffed like Santa's--I joke that one reason I got married is so that I wouldn't have to carry my own luggage anymore. If you are ever in an airport and see a man loaded down like a pack mule, it's quite likely my gallant husband.
*Cashmere travel blanket: Really, any travel blanket will work, though I love the way cashmere is soft and warm, but still lightweight and easy to pack. I got my travel blanket (really an oversize shawl/wrap years ago at Banana Republic, but am planning to "trade up" to one of these at some point: http://www.thepashminastore.com/Cashmere-Blankets-and-Throws-s/22.htm
This is a good lower-priced alternative (not cashmere, but supposed to be very soft and warm!): http://tinyurl.com/32eex3
*Neck pillow: There are multiple options for these in terms of fill and shape, and everyone has a different opinion on which work best. I've tried several kinds, and like this one best so far: http://tinyurl.com/297cqj
It's soft, smushy without ever getting too flat, and the drawstring pouch it comes with can be attached to the handles of your carryon, thus negating the need to make room for it in your bag.
*Ipod: great for enjoying music or just blocking out a talkative seatmate
*Socks: I like kneelength pairs that are a bit snug--keep your feet warm and also keep swelling down by applying pressure. They can also help prevent clots that lead to DVT, which can be deadly (for more info, go to http://www.dvt.net/) And of course, remember to get up and walk around and do some leg excercises every few hours as well.
*Slippers: Great for walking to the bathroom so you're not in there in your socks, or just for walking up and down the aisle to stretch your legs. I find that the free pairs offered in nicer hotels are perfect for this. Besides being comfortable and easy to pack since they're so thin, the rubber soles prevent icky seep through from wet airplane bathroom floors or that Mile High Mojito the guy in the seat next to you just knocked off his tray table.
*Armrest compatible headphones for the movie: Ssome airlines charge for these usually $2-$5 on domestic flights, though they tend to be free on international flights. Either way, hang onto your pairs to use on future flights.
*Books, magazines, crossword or Sudoku puzzle books: To keep your mind occupied! I also carry on my travel journal--great for writing down thoughts, impressions, expectations, etc. of the flight itself and the trip ahead of (or behind) me. My journal has a pocket where I stick our passports, boarding passes, etc., which makes it much easier to grab them when it's time to fill out customs declaration forms and entry documents (which require flight and passport # info).
*Portable DVD player and DVDs (CDs if you don't have an Ipod): Let's be honest here--9 times out of 10 you are not going to want to watch the movie they're showing on the plane. And if you have to go to the bathroom during the movie, you might miss the one good part. Take your own favorite DVDs and solve both problems. Not worth taking this on short flights but great for the longer journeys. These can also come in handy while on your trip. While I am an opponent of TV on vacation in general (though I do adore European commercials for their humor and frequent gratuitous nudity), when the power goes out right after dark (7:30 pm, in one case) during a tropical storm, it's nice to be able to finally catch up on the past season of Entourage.
*Eyemask: Mine is pink and black silk and has the words "Sleeping Beauty" embroidered on it (a gift from my mother-I'm not narcissitic enough to buy that for myself! Though apparently am narcissistic enough to wear it. haha). It always gets chuckles (ok, maybe those are snickers) from other passengers and FAs, but I love the softness of the silk against my face, and the black lining blocks out most light. There are of course thousands of other options, for those who lean towards the more minimalistic or are male. Be sure to buy a mask that fits snugly enough to stay in place without being too tight (must avoid airplane-seat-head!)
*Foam earplugs: nice to have when the guy next to your is snoring or that old lady across the aisle is howling with delight at the in-flight premiere of Cocoon.
*Moisturizer: The cabin air is very dry, so your skin will get quite dehydrated on longer flights. Smooth a bit of moisturizer on your face and hands every few hours, and you'll feel much more comfortable. Also very soothing to put a bit on your feet and ankles--but please perform this task in the restroom, so as not to gross out other passengers.
*Eyedrops/contact solution and case + extra contacts: Again, dry air = dry eyes. And I personally find it's easier to sleep (and gentler on my eyes in general) if I take out my contacts on a longer flight. I also pack an extra pair in my purse/carryon, since I've had a contact or 2 rip from the dry air.
*Purell Hand Sanitizer: because airports and planes are full of germs. Plus, it's a lot easier than trying to get into the bathroom to wash your hands at busy pre-meal times. And once you arrive at your destination, this stuff is great to use to wipe down the remote control, phone earpiece etc.
*Pen for crosswords, Sudoku, journal writing, and/or filling out customs declaration forms: The flight attendants may have one, but they will likely tell you they don't. If they do admit to there being a writing implement somewhere on the plane, you can bet that someone else is already using it...for the duration of the flight.
*Camera: You don't want to check cameras, as they can easily be broken or destroyed. Always carry these on with you. It's also nice to have it handy to take photos as you come in for a landing when traveling someplace scenic.
*Ziploc baggie: For cosmetics, toiletries, and any other gels or liquids. The bag can be up to quart size, and each container inside must be no more than 3 ounces. Here are the official guideline: http://www.tsa.gov/press/happenings/9-25_updated_passenger_guidance.shtm
*Jewelry: don't pack any valuables in checked baggage--they should all go in your carry on.
*Warm sweater/cardigan:just another layer to keep you warm, as it tends to get pretty cold on flights, especially near the exit rows.
*Change of clothing: Especially a bathing suit/cover-up if going to the beach! You'll be glad you packed this when your luggage is lost or delayed. Also good to pack a regular outfit if you are planning to or think you might get bumped from the flight. Most likely you won't be able to get your baggage back off the plane, and it's nice to be able to change clothes if you end up not getting on another flight til the next day!
*A few snacks:peanuts, granola bars, whatever. In case you get hungry between meals or don't want the plane food (assuming there is any, which there's generally not on domestic flights). We also buy a bottle or 2 of water right before we get on the plane. That way, we don't have to track down the FA everytime we want some water (plus I've noticed that many airlines no longer give out bottles of water--only cups).
***A useful website for all kinds of travel products: http://www.travelproducts.com
