Toilet paper. The term "bog" is a British slang for the bathroom, the john, the head, the toilet. And of course, the only "roll" you are likely to find in the "bog" is made of tissue paper. Hence, "bogroll".
"Do the animals here in the zoo have a bathroom?"
"No they just use the ground."
"Well, does they even have a bogroll? You know like toilet paper?"
"No they don't need it."
"How do they clean their butties then?"