[Ziv]

Getting a robot to reliably drive to different coordinates on the field autonomously (by whatever means necessary) is useful in virtually every game's autonomous mode. It's a challenge that requires relatively advanced code and a lot of debug time, making it not the sort of thing you want to do in the possibly short time between robot completion and bag day.

It seems like FRC is making camera tracking with retroreflective targets a thing, so getting some experience with that in the offseason could be good. This is especially true if you want to do fancy math on the targets to get their position in space.

By contrast, light sensors tracking game pieces could be useful, but the main challenge here is in the logic; once you have the right program flow, a ball elevator (for example) doesn't need too much tuning. Shooter wheels are the opposite; the programming logic is mostly simple but requires a lot of testing. Both of these are game specific, too.

TL;DR: Slap some encoders and a gyro on the drivetrain and make it dance!