What item can't you live without that no one else seems to know about?
Small corkscrews are fine in US airports as long as they don't have the foil-cutting blade. Mine has never been confiscated by TSA. (Although since the recent small folding knife melee, maybe they've changed that, too). But keep in mind that different countries do have different laws. What's good or bad in the USA might not be in Spain or South Korea or Great Britain, etc.
So you might take your little, bladeless corkscrew with you from the USA to some other country without a hitch, but have it confiscated on your return trip.
I have one of those little Belkin 3fers, it's handy but heavy. As in, quite heavy and could easily pull itself out of a wall socket. Nowadays you can buy small 3fer outlet strips and also little 1 and 3 foot extension cords, because instead of everything needing AA batteries like the old days, now you need access to AC power all the time and lots of it. A 3fer outlet can also be very good in the airport or train terminals, where if you look for the scrum of people squatting on the floor you can tell where the wall outlets are. There are never enough.
You'd also have to be crazy not to travel without several pairs of ear plugs. And I have a white noise app I loaded onto my cellphone that works quite nicely. Also put a flashlight app on your phone as well as bringing several flashlights. The other standard recommendation was a golf ball, to use as a drain stopper in sinks and tubs. Probably easier to carry one of the flat rubber varieties but whatever.
I would always have at least 2 Swiss Army knives in my bags but nowadays it's so risky, you never know what will catch the TSA's eye or when.
LED for when the lights go out - never leave home without at least one hanging from a beltloop - this one from www.photonlight.com
I always take a small battery powered tea light candle. It's a great nightlight and doesn't require an outlet.
A clothes pin to hold curtains together at night when they insist on a gap
A folding shopping bag/backpack
I know this is an old thread, but this is just too rich not to share.
An acquaintance of mine recently came back from Spain--her first overseas trip. She paid excess luggage fees to take two cases of Coca-Cola because she heard that Cokes were expensive "over there" and that different countries have different formulas that affect the taste. Talk about your brand loyalty! Towards the end of the trip, she ran out and had to drink the local version--she was somewhat disappointed that she could not discern any major difference in taste.
I do live in a extremely culturally deprived and conservative part of Maryland. Let's just say that culinary and beverage preferences are a tad insular. But, to be fair, people are nice, and it is a very safe place.