Some good ideas already in the thread. Waco has a few things to do that are interesting and has gotten much better for visitors / tourists since the Magnolia place opened a few years back.

Besides the Dr Pepper Museum, there's obviously Magnolia which is also in downtown. It's insanely popular and changed downtown Waco (for good, for the most part). They sell home goods I believe, but there's also a restaurant / cafe.

Baylor's campus is pretty as well and fairly walkable. Obviously, there's the new football stadium and some walkways along the Brazos River. The Armstrong Browning Library and Museum is a quick visit, but worth considering. On Baylor's campus there is also the Mayborn Museum complex. There is a natural history portion that is not bad. The Texas Sports Hall of Fame and Texas Ranger Museum are both right in downtown as well, right by the Mayborn Museum, the football stadium, law school, and the football complex.

A few minutes out of downtown Waco is Cameron Park and Cameron Park Zoo. When we lived in the area we'd take our kids to the zoo frequently.

One thing unique to the Waco area is the Waco Mammoth National Monument. I'd recommend visiting.

And as someone else suggested (especially if you're coming from DFW), stop in West and get a fruit or meat (or both) kolache. The Czech Stop and others are right off of I-20. We always made it a point to stop and get some kolaches. Have them heat them up - they taste better warm, IMO.

Enjoy Waco!