Which four?

[Vierings]

FAK-obvious reasons
knife- use it for making other tools, food prep, possibly as a reflective device, starting fires if there is antiquate other materials and may other uses.
Tent- its obvious use is shelter, but you can can section it out for other things, like rope, sling, shelter, boat, sail,making clothing, ect. the tent poles could be very multi use as well, spear, cooking utensil, ect.
Pot- water purification and cooking.

If I were to add six things..
boots
saw
compass
raft
flare gun
rifle

 

[mkwerx]

FAK
Cooking pot
Hammock
Fishing rod

Expanded list adds:

Hand saw
Tent
Knife
Tarp
Rope
Rifle

The fak is important for sure - if you just survived a crash you are likely banged up.

The fishing rod will aid in food gathering. I will assume theres tackle with the rod - and the line is decent.

The pot will boil water and cook dinner. Indespensible. The hammock will keep me off the ground and provide comfort - which is good for the body and mind.

Expanding the list - the saw will aid in constructing shelter or an eventual resort should i decide to stay and become an entrepeneur...

The tent will provide shelter from the sun. The tarp can be strung over the tent to shelter from rain or be used to cover the tiki bar for the above mentioned resort.

Rope will aid in shelter construction and possibly secure any female that happens to wash ashore on my little fifedom. Can't repopulate the island by myself!

Knife to clean the fish - beats a sharpened rock I'd be using if stuck with only four tools.

The rifle can gather food - fight sharkmen - or enforce order at the resort if happy hour gets too crazy. Besides chicks dig a crazy island guy with a rifle...