As you say, bad luck and a big bad weather front would be a drag, but at least nowadays it's fairly easy to get really good predictions and weather radar access on line, so at least that helps a bit.
Re shower caps, I've used a few and they really do work well. Ended up getting as a gift one of those yellow ones like tourist msn, which is tougher than a hotel thin one and I feel the yellow helps cars to spot me too in bad visibility. It's really nice not having rain run down your hair in your face and down neck.
Also like Tmsn, I often use a neckup or neck gaiter, keeps neck and shoulders from getting chilled and stiff.
Dishwashing gloves may look goofy, but they saved my arse on one long, cold wet day where I had no choice but to ride. Would have had wooden fingers if not for some light wool gloves inside the dish gloves. A bit goofy but believe me, that day I couldn't care less.