How can I charge my MacBook Pro and not block one thunderbolt 3 port for other uses?
Solution 1:
Apple makes a USB-C Digital AV Multiport Adapter which you can use to connect a USB-A thumb-drive and power the computer simultaneously. Other manufacturers make similar devices, but Apple's offering is well-made.
All sorts of hubs exist so you can pick your price point, support, features and decide if a larger, more rugged device is less likely to disconnect while the event is happening.