OK, right: looking for a merging of stars would be a terrible anomaly to use because that's probably classical mechanics and Omega-predictable. The milk unspilling would still be a good example, because Omega can't see it coming either. (He can accurately predict that I will two-box in this case, but he can't predict that the milk will unspill.)

I would have to be very careful that the anomaly I use is really not predictable. For example, I screwed up with the streaking star. I was already reluctant to trust flipping quantum coins, whatever those are. They would need to be flipped or simulated by some mechanical device and may have all kinds of systematic biases and impracticalities if you are actually trying to flip 10^23^23 coins.

Without having plenty of time to think about it, and say, some physicists advising me, it would probably be wise for me to just one-box.