My BOB holds an eighteen gallon tote. I usually use the tote around town for trips to the dumpsters, recycle center and stores. I do take the critter to the vet---in her "room"(crate) covered with a blanket in cool weather. She loves to ride.
I live in rural Georgia. That means you have to have a dog to protect your trailer house against thieves stealing the nothing you have. It's funny when they run out to bark and chase the bike away and the bike barks back......stops the "killer" watchdogs in their tracks.