In Sumter, go south on Highway 15, toward Paxville. On the left, somewhere between Paxville & Sumter is a little restaurant called "Country Fixins". Unbelievable southern food, all you can eat. The Guignard Diner on Guignard Dr., over by Stanley Welch's and the Rustic Market is really good, and serves good southern food. Actually, the Rustic Market is great for fresh produce, frozen casseroles, garden supplies/plants, etc. Red Bone Alley is good, they are a southern chain restaurant based in either Sumter or Florence (I forget)
Ward's BBQ has mediocre BBQ, but excellent hash and rice. The Sumter area has some really great BBQ joints, but they tend to open, close, move, and change names over the years. There used to be a great one called "Southern Pride BBQ," but it may not still be open.
Shuler's on North Main is a great dairy-queen style place, with good hamburgers.
Mary Ann's Deli on Bultman Drive is a good deli/sandwich shop.
Sambino's, over by the YMCA on Miller Rd. has inexpensive, pretty good Italian food. Georgio's is also good, I think they have a few different locations.
The Mill Pond Restaurant is a rustic old country store, converted into an expensive restaurant. It's in Boykin, about 20 minutes from Sumter on Highway 261. Lilfred's is another really nice place in Rembert, on Highway 521.
Zaxby's and Chik-fil-a are two great fast food chains that serve chicken sandwiches, salads, etc, both on Broad St.
If you want a place where people hang out on Saturday night in their cars, go to Sonic. Not exactly a mom & pop diner. Big Jim's and Cole's were two of the popular old school hangouts in Sumter, where 40 years ago, people would hang out like you said. Big Jim sold out to someone else, and I think it is still open under a different name. Cole's is now the Walgreen's on Broad. A lot of the ladies who cooked at Cole's went to work at Buster's, on the corner of Wesmark and Broad, which I think is still open.
There was a thread a while back on Columbia's restaurants. Sumter has the basics, but Columbia has a much wider selection, particularly with fine dining.
http://www.city-data.com/forum/colum...-you-love.html