It depends on the riding they do. I like to do a lot of long distance riding, and I can never have enough good luggage. Tank bags, small waterproof duffel bags, sissy bar bags. Different shapes and sizes for different occasions, it's great. Perhaps an 'upgrade' to some of his/her existing stuff? Hard bags to replace soft bags, fairing to replace windshield, etc?
Or maybe even something for the rider! I'm asking Santa for new motorcycle boots this year myself. Maybe some new gear for winter riding or a nice new set of gloves or boots or something?
"8 But God demonstrates his own love for us in this: While we were still sinners, Christ died for us."