In October, my choice would be the multi-climate choice of weather jacket (Patagonia, in my case) that I already wear around town when it turns rainy or chilly. As mentioned above, ponchos are like trash bags, and after the rain stops, you get to throw them away because they cannot be refolded into the same compact package they arrived in. They become a wet trash bag, balled up on your day pack.
We were in a rain shower in Sorrento a week ago. Within a minute of its beginning, she shopkeepers began to display trays of ponchos and umbrellas (3 euros apiece for the umbrellas; dubious quality, but they worked in a pinch) for sale. After the rain showers passed, there wasn't an umbrella to be found.
I travel with a good quality windbreaker which doubles as an all weather jacket. I brought a good quality travel umbrella from home, but it was usually in a suitcase back at the hotel when rain threatened. I am rethinking that packing choice.