How do say toilet paper in Chinese?
In Hong Kong "Toilet paper" is simply called 廁紙. 

Before the modern toilet paper,  people were using 草紙(rough straw paper) for toilet paper.

As for a roll of toilet paper , it is still called " 廁紙 " ( with classifier if needed. For example  一卷廁紙 ) and the more technical term would be 卷裝廁紙

For tissues in a box, we call it 紙巾 (with classifier if needed. For example 一盒紙巾)and the more technical term would be 盒裝紙巾 

*衛生紙 is another name for 廁紙 or 紙巾.