(Note: These rules began as a series of preflight tweets at pwilke that I have since expanded upon below)
Rule #1: You can never have too many sets of headphones on you. Normally I carry about three sets. This rule is more related to my own phobia that came out of a trip to rural India, where I accidentally left my only pair of headphones on the plane. You haven't lived until you've gone headphone hunting in a town that didn't have too many iPods back in the day. Bottom line: headphones don't take up a lot of room, and they're easy to lose. Pack a spare pair.
Rule #2: The toiletry you need on the plane is the one you didn't put in your carry-on. This should be fairly self-explanatory, but if it's dental floss you need? It's in the bag you checked. Cut your finger? The Band-Aids are in the bag below, but you can bet your ass you have your Blistex and deodorant in your backback (and won't need them mid-flight).
Rule #3: The longer the layover, the less interesting the airport. This is just a slight variation of Murphy's Law. I once had the misfortune of having airport wait in iPoh, Malaysia for eight hours once. And this was in the days pre-dating iPods...and it was the last time I ever flew without being armed with reading material. Ipoh is why I carry batteries, magazines, food, water and cyanide tablets in my carry-on bag.
Rule #4: Follow your gut, senses and any kind of profiling you prefer when deciding who to stand behind at immigration and security...just know that whatever system you use will probably be wrong. When I was living in Singapore, I used to always say, never get behind an American ordering coffee at Starbucks. Same sort of rule applies to immigration and security. You know who's going to be difficult in this situation...look before you commit, but just be prepared to be unpleasantly surprised.
Rule #5: The longer the flight, the stickier the food or liquid you'll spill on yourself. For years you could set your watch to the fact that if SQ was serving satay on a flight, in minutes I'd spill peanut sauce on my clothing. Orange juice is another guaranteed spill culprit while flying. If it's a short flight, I'll likely spill water on myself, anything longer than an hour, I might as well just dump a jar of Fluff on my head, since whatever I spill on myself at that point will have the same effect.
Rule #6: Business class lounges prove that, yes, you can make a filling meal of Bloody Mary mix, saltines and Milano cookies. Business class lounges around the world are like snowflakes...each one is different, but they do share a common bond...each has an array of food you might not eat elsewhere. I've snacked on gummi bears and pretzels care of the Frankfurt business class lounge, Milano cookies in LAX, Pringles in Madrid and, well you get the idea. The food you want isn't always going to be the food you'll find in airline lounges, so you make due with what's there. And does anyone really eat the little nondescript sandwiches they serve?
Rule #7: Always have 2 magazines in your carry-on. One for takeoff, one for landing & the remainder of each for when your iPod batteries die. See rule #3...and never underestimate how long the time between the plane door's closing and the "ok to use electronics" all clear is sounded takes. And realize that the inflight magazine and SkyMall catalog just isn't going to cut it for takeoff and landing.
Rule #8: If they're offering you water on the plane, take it...you never know when they'll offer it again.
Rule #9: Skip in-flight breakfast. It never lives up to what you want it to be. Eggs and sausages lose something at 30,000 feet...namely flavor. Skip it. Although...on my flight the other day, Singapore Airlines handed out Krispy Kreme donuts - a step in the right direction.
Rule #10: Be kind the to the flight attendants...their job is harder than you can imagine. No one particularly likes what flying has become with added security checks, fewer luxuries and increased rules and regulations...as hard as flying has become for you, imagine how much difficult it is for them. While you're relaxing mid-flight, they're working their tails off. They're trained more than to just find you a pillow...they're the conduit to saving your life in case something happens...and that covers a lot of ground. Be polite, considerate and let them know you appreciate what they do.
Finally, and this was originally a rule, but I realized it more a mantra: No matter the destination, you're traveling...make the most of the adventure!