Most everything good has been covered already. Check out the National Cemetery and the spot where Abe gave the Gettysburg Address.
Gettysburg CG is nice and if you have a problem, JRs RV service is right there and you will receive top notch service at a fair price! We like to weekend at Artillery Ridge. I live less then a mile from Drummer Boy and can smell the campfires most nights in season. It is a nice campground as well.
When touring in town as a pedestrian, please heed the crosswalk lights and use the crosswalk. I can't count how many tourists have been hit in the last ten years because they jaywalk or are impatient for the light. Another side note. Be prepared to pay higher gas prices here in Gettysburg then surrounding towns. Even now we're .10 higher per gallon then the next town over.