We camped at Halfway Creek in the Francis Marion National Forest for the eclipse. It's a free campground, but there are no water and no toilets. You can park in a lot just outside the camping area--some people sleep in their cars there. This site does not take reservations, so it's first come-first served.
The actual camping area is wide open and grassy, but if you prefer more privacy, you can hike in a bit and pick a spot. We stayed in the open area because we were a big group and wanted the best view of the eclipse!
Something fun to do is to visit (gotta drive there) the Halfway Creek Church, constructed in 1941. You can also do a hike on one of the trails here.
Bring lots of water and bug spray and some trash bags to pack your trash/T.P. out!
[Off Halfway Creek Road (SC Route 98-S), located along Swampfox Passage/Palmetto Trail]