At the Spearfish campground, be sure and check out the adjoining US Fish Hatchery. great place to wander about and is right at the campground.
Other places, leave the entrance and go about six streets north on Canyon St at W Illinois is the neatest, cleanest laundry you ever saw if you need to run your laundry. One block over on W. Illinois and N 5th St is Stearfish Steak and Smoke. Pretty nice and good food, though somewhat expensive. Continue North on Canyon one more block past the laundrymat and turn left on W Jackson, cross the creek and around the curve and at the light make a left on N Ames. You find Dough Trader Pizza. Good local pizza, again somewhat pricey but good.
From the campground, walk into the park and over to the creek. There is a paved walk that goes for a number of blocks along the creek, nice evening walk. Very safe.
Go east on E Colorado (Alt 14) or the interstate one exit. The Wal-Mart is on the north side of the interchange and if you continue on E Colorado and turn south on Heritage you come to the High Plains Western Heritage Center
http://www.westernheritagecenter.com/Also on the south side of the interchange is a Pizza Ranch. I have not tried it but lots of folks rave about it.
Don't forget the Journey Museum in Rapid City, its well worth the 50 mile drive from the campground.
Charles