I used a lightweight cotton hoodie when it was sprinking. Being that it was cotton, it didn't dry fast, but I was able to take it off and tie it around my waist or ball it up into my bag pretty easily.
I strongly advise against the dollar store poncho if the rain is anything significant. In the past, we bought heavier Coleman ponchos for around $5 each at Big Lots. They worked great and really kept us dry. Last year, we opted to buy the Disney ponchos when we needed them which were around $9 each I think? More expensive, but we were able to wait and buy them when needed and surprisingly, they worked really well. Much better than the dollar store ones which are short, sleeveless, and have no adjustment for the hood so if you have hair - it will slide right off.