A good round needs less than the industry would have you believe. The useful additions are usually quiet and portable, each solving a small problem without turning a walk into a packing exercise.
1. A proper rain layer. Not because rain is romantic, but because being prepared changes the mood before a cloud has even arrived.
2. A small notebook. Scorecards vanish, memories blur and a few lines after the round will outlast most swing thoughts.
3. A bottle that keeps water cold. It is a small courtesy to your future self on the back nine.
4. A towel with some life left in it. It does more work than almost anything in the bag, so it should feel good in the hand and be easy to find.
5. A ball marker you will not lose. Choose one with enough weight and a little character. The point is to stop looking for it.
None of these things will change your handicap. They will make the day run more smoothly, which is often the more useful kind of improvement.