Ask HN: Travelers of HN What's the Most Useful Thing You Own?

A Costco mixed nut container. Eat the nuts, scrape off the label, and you've got something more useful than a typical packing cube. You can densely pack clothes in it, or use it as a catch all container for loose items. It's clear, so you can pick the items out easily (and the bureaucrats can inspect it), and it's rigid, so things won't get banged up. When you're at your destination, you can use it as a general purpose storage container. It also fits under your airplane seat so you can use it inside your "personal item".

I have a satechi power adapter that has four USB ports (3xA, 1xC) and a removable cable that goes to wall power. It is uncommonly useful because it charges everything I own from one wall plug, and because I can swap the cable that goes from wall to charger to support the country I am in. This means I don't need wall-wart plug adapters.

A smart phone is probably the most useful travel item, but I can also highly recommend an Aero Press for good coffee while on the road. I finally got fed up with bad hotel coffee and got one, and I am seriously impressed! Pair that with one of those small portable water heaters and you can have a good cup almost wherever you find yourself.

Adding to the other great answers- a multitool, a bigger one if you can allow it for example when travelling by car, a small one or even knife-less like the Leatherman PS if you fly.

My tiny Victorinox Classic saved so many times- cut nails, loose wires or fibers, fix glasses, fix broken zippers, treat small wounds and splinter etc.

Not a very creative answer, but a smartphone with an international data plan and large battery is probably the best tool in existence.

I guess a universal power outlet adapter is pretty helpful too.

Cash.

The only things you'll really need when traveling are:

- 3 changes of clothing appropriate for the weather

- Solid shoes

- A coat or jacket

- A durable bag

- A good hat

- A toiletries bag

- Ear plugs and a sleeping mask

- A charger for your gear, and cables

- AC power plug converters

- Maybe a battery

Everything else is situational, and better bought on the spot.

Credit card. Cellphone. In that order. (I only travel the parts of the world where credit cards and cellphones work)

Noise canceling headphones.

a good knife.