After 40+ years of tramping etc I still find it useful or at least reassuring to at least glance at a list before heading out the door.
There are plenty of (good) opinions out there, every overnight trip is slightly different, and with in each category (or line in this list) there is usually many choices to make ... but everybody I know would probably tick at least once for most of the following lines ... on most trips ....
pack / waterproof liner(s)
boots / gaiters / walking shoes
sun hat / sunglasses
rain jacket / overtrousers
warm hat / gloves
light spare clothes (for evening/sleeping)
ground sheet / mattress / cover / fly / tent
cooker / fuel
bowl / mug / plate
head torch / spare batteries
...PLB (at least one per group is fast becoming the norm).
tooth brush / paste / soap / towel
first aid / spares and repairs