According to the Mountaineering: The Freedom of the Hills, the ten essentials of HIKING are:
1. Map
2. Compass (optionally supplemented with a GPS receiver)
3. Sunglasses and sunscreen
4. Extra food and water
5. Extra clothes
6. Headlamp/flashlight
7. First aid kit
8. Fire starter
9. Matches
10. Knife
There are many variations on the “essentials”, of course, many combining matches and fire starter, many adding “shelter”.
Personally, I refer to a much more practical list. One put together by Tom Mangan for day hiking in reasonable weather:
Mangan’s 10 Essentials for Happy Hiking
1 – A water supply
2 – A reliable map
3 – Comfortable socks
4 – Comfortable shoes
5 – Underwear that doesn’t chafe
6 – Something to keep crud out of your shoes
7 – Nylon hiking pants
8 – Something to block the sun
9 – Nourishment
10 – The Real 10 essentialsTwo-Heel Drive – Mangan’s 10 Essentials for Happy Hiking
Leave a comment if you have any ESSENTIALS for day hiking that are not listed.
besthike.com 
The 10 normal essentials +
A cushy sit pad.
Microspikes for off season.
Stove.
Pot.
Spoon.
Nature book on flowers.
A small tarp for lunch in bad weather.
Gaiters to keep junk out of shoes.
Gourmet food to cook for lunch.
A cushy spot to take a nap in the sun.
😉
Ha, I like it Sarah !!
Personally, I agree with all of these except GPS and nylon pants. Both are largely unnecessary in my opinion, although very nice to have.