there is watercraft available to be rented though i cannot recall exactly what kind. i think they were kayaks or conoes

Sorry, we did not camp at Sylvan Lake, but you can get information about camping throughout Custer State Park by searching "camping Custer State Park South Dakota" and you will see an official state website (which I was prohibited from providing as a link in this answer). Tony

I didn’t camp there we only hiked around the lake.

Yes. There are lots of places to set up a grill.

I don't believe so, but there is a small sandwich shop/snack bar at the lodge.

You might call some of the fly shops around Custer or Hill City

If you do bring a dry suit, it’s really cold.

You can rent small boats and paddle boards at the store right at the Lake. Only open during season. No gas powered boats are allowed. Very small lake but absolutely beautiful.

It is per car! So it’s worth it ! If you are doing to visit other parks around the area find out how it works because I believe that you can use it for other things also . Don’t remember now. Have a great time !

Sylvan Lake is free but to get there you have to pay entry into the Custer State Park which is $20 per car