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) there is often many choices to make ... but everybody I know would tick at least once for each of the following lines ..
food
pack / waterproof liner(s)
walking clothes
boots / gaiters / walking shoes
sun hat / sunglasses
rain jacket / overtrousers
warm hat / gloves
light spare clothes (for evening/sleeping)
sleeping bag
ground sheet / mattress / cover / fly / tent
pot
cooker
lighter
bowl / mug / plate
spoon
head torch / spare batteries
pocket knife
map, compass
...PLB
tooth brush / paste / soap / towel
first aid / spares and repairs