Based on Richie's role as an accomplished event photographer who spends a lot of time kneeling down and running to capture moments, the equipment he would most likely bring would need to be versatile, portable, and allow for quick adjustments.
The best option among the provided choices is:
interchangeable lenses, a backup camera body, and a flash unit
This selection offers the versatility needed for different shooting conditions at events, reliable backup equipment in case something goes wrong, and a flash unit for varying lighting situations, which is crucial in event photography.