There was a time, years ago, when Disney still sailed to Freeport, Grand Bahama Island, that there were ponchos onboard, available for purchase.
This was also the time, when Disney was, in my humble opinion, still trying to win over people to sail on
DCL. Or Disney was just different then, I don't know. Either way, we arrived into the Freeport port, and it was pouring rain. Upon entering our cabin after breakfast, everyone had ponchos on the bed, gratis from DCL. They were also handing out a limited amount when departing the ship, if you didn't get back to your room after breakfast. Same ponchos that were sold in the parks.
We still have those ponchos!
I highly doubt DCL would do this again. At least, not on the Dream!