Since it is currently only used for fast travel, here are some suggestions of what else you could do there:

- Healing
- Staying overnight
- Cooking
- Fishing (if there is a pond/water nearby)
- Learning about Zant Lore (if there are characters on the wall nearby or just Sparky telling us)
- Learning Ancient Language so that you can read the characters on the wall
- Having hangouts with Sparky
- Making fast travel possible when using the campsite, not just via the map
- Cleaning yourself (clothes could get dirty over time in the cave, or generally give a short buff), 'tuning' or polishing Sparky and giving him a short buff
- Training (friendship with Sparky could increase because he is a sparring partner, stats could improve, short buff because of training)
- Praying, and thereby strengthening Ofuda, Omamori, and Dorei for a time