I use a Showers Pass Elite 2 rain jacket. Not that packable, but it is my commuting jacket and I wear work clothes under. Way back, I use to pack those souvenier tyveks on touring/training rides. Often we would put them on backwards to cut wind chill. They roasted you, though.

I also found rain showers were not so bad, mostly it is being able to keep the extremities and core warm -- and hope you don't have to stop for too long.

Good luck.