It often depends upon the season and the locale. In most of Canada, for example, you won’t have to worry about a desert environment or protection from extreme sun, but in large parts of the USA in the summer time, those are real concerns. So for most of Canada, then “water purification / filtration” is fine, but in a summertime desert environment “water itself” is a necessity. (That would also apply in a marine – salt water – environment, obviously.)
But in general:
shelter of some kind, even if it’s just a mylar blanket or ground cloth
water or water purification / filtration
a knife (or more than one knife)
waterproof matches and storage or a flint and striker, plus tinder
change of clothing and several pairs of socks
para cord
compass
these days, a phone charger and spare USB cord
LED flashlight (specifically “LED” because they’re better on battery life)
med kit
Again, depending on the environment and season, it might be wise to include some dehydrated or bagged and ready-to-eat food, but not a lot.
Whatever you need specifically that you can’t easily acquire, such as prescription meds.
I’d pack spare readers for myself.