There are other of options for stowage on a road bike, even if you don't go with a rack and pannier. You can get a large under the saddle bag like this one:
https://www.ebay.com/itm/Bike-Saddle...EAAOSwNpdct-8S
There are top tube bags like this one:
https://www.ebay.com/itm/B-SOUL-Bicy...dWEP93Y3QjHctA
But if you have to carry lots of things there's nothing like a full rack and panniers.
