There are 3 main Wal-Marts availiable to Clemson students. Each one is a Super Wal-Mart, offering groceries and everything else you'd expect from the world's most hated super center. If you're looking for something a little higher-class for cheap furniture or clothes or something, you might try Target. Ranked in rough order of popularity and closeness, they are:
To go to Central, take US 123 north/east, towards Easley or Greenville. If you're coming from downtown, make a right at the light. Pass the exit for Issaqueena Trail. The next exit is about a mile further; take it, make a left, cross the bridge and the Wal-Mart will be on your left. This is the newest, with construction just completed in 2004. It's about 5 minutes from campus with no traffic.
Take US 123 south/west towards Seneca. You'll cross the lake, hit some traffic lights, and a few minutes later Wal-Mart will be on your right, more or less across from Fatz Cafe. It's a big green building. This one is about 10-12 minutes away from campus with no traffic.
Take US 76 east, towards Anderson and I-85. Cross over I-85, go past the Honda dealership on your right, and a minute or two later the Wal Mart will be on your left. This is the oldest and most decrepit of the Wal Marts in the immediate area. It's about 15 or 20 minutes from campus with no traffic.