Long term storage of things digital

“Digitalisation” is a buzzword in the humanities, closely connected to the Digital Humanities, to open access, reproducibility, sharing heritage and so forth. I believe it is a very important step to a better and more open science. There is one point though, that is important to me: I’ve worked with books 115 years old. How can we make sure people will be able to read our digital output in another 115 years?