It makes sense to carry a few small items on the golf course:
Most players also carry a towel to wipe their clubs - a professional will expect his caddy to do it after every shot.
It only needs to be small but you may need a couple when it's raining to keep your clubs dry.
These are useful for protecting your clubs from knocks.
This is used to repair pitch marks on the green. A tee can be used instead if you don't have one.
Many golf gloves include a small pop-off marker on the wrist which can be used to mark the ball on the green.
But you can use anything for this job - a small coin such as a five pence piece works just as well.
Pencil and scorecard
For keeping score and making notes about the round.
An average round of golf takes at least three hours so you will want some kind of extra protection during heavy rain.