I am still adding to my bike, with the highway pegs being first and then moving to areas that have to do with safety/visibility. I added a rear wing with modulating brake light, mirrors with the turn signals built in (muth signal), and driving lights. The cup holder I see as very important for riding in the heat - dehydration can get you before you know it, but of course a CamelBak would beat that.
Bottom line, there is always something to add.