I carry a spare 25' 30A cord, along with a spare water and sewer hose. When travelling with friends, we like to orient our RVs in a social setup, either facing each other, or in an L shaped setup. This often means one of us is not near enough to the hookups to connect without them. Plus, having a spare is nice.
I only carry a short 15A cord, and this is mostly for getting the small electric kettle to reach the table outside, for morning coffee.
I could get a 30A twist to 15A, a 50A to 30A, and an additional longer 15A cord, but my plan is to not become a hardware store.
Many would not likely bring the spares that I do either, we each have our own styles.