The old adage of baking once and eating twice can be very safe with just a few precautionary steps. I leave off things like rolling the potato in oil or other dairy coatings like melted butter, so that there is no residual that could be a food safety issue when the left over baked potato cools off. Once the potato is baked, cut it in half and let the un-topped portion you plan to use tomorrow cool slightly from the oven, then place into the refrigerator and cover with a clear plastic wrap or a towel.  The food safety issues that can be a problem results in baking a potato in foil, adding something like butter and sour cream and then leaving that potato out or wrapping up in foil while still warm.