The rule is fit, not features
A kit you leave at home because it is heavy protects you from nothing. Everything below was chosen because it is small enough that you stop noticing it, which is the only reason any of it actually gets used.
Five is roughly the limit. Past that you are packing a second bag inside the first.
What goes in
Something to feel clean with, which for most people means a portable bidet or nothing at all. Something for the lips, because they are the first thing to go in cold or air conditioning. A fragrance you can top up with. A scarf, which covers cold shoulders, tied hair and a bad hair day at once. And sunglasses, which do more for a tired face than any product.
Notice that four of the five do two jobs. That is the test for anything you are thinking of adding.
Restock before you run out
The failure mode of a small kit is a container that is empty when you reach for it. Refill on a fixed day rather than when you notice, and it stops being something you have to think about.
That is the whole point of an everyday essential: it should be boring, present, and never a decision.
