What’s a super-useful item one should carry with them at all times, since you never know you could need it?

Due to TSA and other post 9-11 realities, I can't carry my usual Victorinox pocket-knife which I use almost daily. It's on my key ring.

I'm a minimalist. Except when I travel. I do bring many tools which don't, at first, seem like tools. A lighter, or matches for example. I was mocked for this, given that I don't smoke, but then some arse needed to see addresses on mailboxes in an unlit niche. Guess who had a lighter? I carry a small compass when I travel since heading in the right direction in the first place saves a lot of time and gasoline. I also carry a handkerchief and long neck scarf when I travel or when I'll be out of the house most of the day. These are useful in a variety of unexpected circumstances.

/r/AskReddit Thread