Cheers, Dave.
If this was an army list it would come with a handy mnemonic. And it would not mention specific items. Instead it would be based around functions. And there would be five plus or minus one of them, so someone as dense as me would stand a chance of remembering the list.
Back in the Sixties, when I began hill walking, the BBC had regular items on people going into the hills in gabardine, jeans and fish tail parkas. They made the news by dying from hypothermia in foul, not freezing, weather. So, whatever it takes to stay properly dry would be my number one essential for British hills. Nowadays, I would regard the old school coat and plastic mack combo I used for my first winter in the Lakes as inadequate.
Having attempted barefoot walking and hit the deck hard, long before I stubbed my toes on anything, my second essential would be whatever it takes to stay attached to the terrain.
There probably aren't any other essentials for shorter walks other than the fitness and good sense mentioned previously.