I rate a headlamp and trowel are absolutely essential. I use my headlamp on many hikes - I finish in the dark fairly often, even when that wasn’t the plan (cough, cough, last Saturday). A trowel is important from the aspect of leaving no trace.
Hmmm - top non-essential items:
- GPS, not always non-essential, but on routes I have done many times before, I often just use it for statistical purposes
- An air mattress for sleeping, I guess out of winter this is non-essential, but a good night sleep helps a lot.
Context: I leave my gloves at home outside of winter to make sure my pack is nice and light.