Which is your favorite gadget?

My criteria may be a little different from someone else's, because I have traveled full time for nearly 3 years, and carry my paragliding gear with me so that I can fly at sites around the world.

That said, my focus is on carrying only things that add enough value to my life relative to my weight that I'll never regret carrying them.

I have to start with The World's BestTravel Adapter.
I've tried probably 20 different travel adapters, and this is by far the best. I wouldn't even consider switching to something else. It's tiny, it's flat, it flexes and folds and reshapes like a freakin Transformer, and it looks like a spaceship. Also it's $10. You owe it to yourself to buy one. You owe it to your friends to buy them one.