What exactly do you mean by "research/professional development and training"? It's a rather nebulous descriptor there - hard to know what you have in mind.
From my impression, there are two main categories of things that seem to stand out to registrarship programs. No. 1 being writing or performing some research and No. 2 being extracurricular training sessions to do with the field. The reason my question may seem nebulous is because the information out there regarding becoming a registrar is really nebulous, dense, and hard to find. The main point of my question is, what can a medical student do to set themselves apart and have a higher chance of getting into a registrar program.