Lonely Planet advises people to carry tissues with them in case there isn't any toilet paper
Toilet paper isn't always provided, so it is always a good idea to carry tissues with you. You may also be given small packets of tissues on the street – a common form of advertising.
I can vouch for small packets of tissues being a common form of advertising, but a lack of toilet paper, not so much. Maybe the author of that advice got the wrong idea of what people use the tissues for.
Is lack of toilet paper a common occurrence in Japan?