We supply lots of first aid kits to people using them in isolated areas and I really do not think any two are ever the same. Except for the guy who has a spec and buys those kits by the dozen!
Things I would put in a kit (just for conversation sake):-
Gloves, several pairs each in their own packet.
A bag valve mask (not first aid but this is my list).
A disposable suction device (as BVM).
Some airways (as BVM).
A chest seal.
A tourniquet.
Some big and medium dressings and some gauzes.
A pair of rescue shears.
A roll of SAM splint.
An instant ice pack (might have to remove and restock if flying).
Some tapes.
Some wound closure strips.
A procedure pack.
Some tipet sachets and saline pods.
A stethoscope & sphyg.
A foil blanket, glucose sweets and a couple of glow sticks.
But as has been said, anyone experienced is going to have their own list. Some bigger and some smaller than this one.