Some lesser thought of items I’ve picked up along the way:
– Empty ziplock bags
These tend to come into handy for so many things – sneaking snacks out of a breakfast buffet, needing to pack wet clothes quickly, holding anything that breaks, etc etc. I always have a dozen in different sizes
– A big swiss army knife (obviously in checked bag)
I’m constantly in need of a bottle opener, pair of scissors, or a mini screwdriver
– Chain bike lock
For backpacking or less secure travel, I have a suitcase that locks, that I can then chain to a piece of furniture, or a luggage carrier on a train or bus – nothing is 100% but it definitely adds a good layer of security.
– My own pillow
I’m just really into my one particular pillow that I sleep with every night. It’s squishy and compacts into my carry on fairly easily. I pretty much never leave home without it.