Rocks DO need backing up. Scribes in Sumer maintained traditions over thousands of years of recopying clay tablets to preserve them. Even the ancient Persian conquerors of Babylon constructed museums of the already very ancient objects they found there. The same was true of later scribal traditions on leather and parchment which preserved classical documents for us, and the ways of reading them. In fact, if it weren't for the far superior concern for posterity the middle ages showed, we would not have the smattering of knowledge about the classical world we have managed to hold on to.
I am a linguist who studies clay tablets and ancient writing systems, and let me tell you, I lose sleep over this problem every day. What will happen (and note that I don't say would, because it is inconceivable that the "cloud" will last a thousand years, let alone five thousand) when they don't know what kind of electricity we used? Where will the remains of our civilization be? There is a basic point here which the "wayback machine" doesn't go far enough to answer. Where will they find our information stored, and how will they ever, ever, devise a way to read it? Bear in mind that we have trouble deciphering the earliest and most primitive writing systems ever devised even now. There are still dozens of these we can't read, and many more we haven't even rediscovered yet.
And, it turns out, a lot of what has happened to survive for us to read from all that time ago really is about as exciting as server logs - receipts for tithes, buying and selling grain, etc. And those tell us so many surprising and extraordinarily valuable things about the way the people who produced them lived, which the documents they intentionally preserved (such as king lists, prayers, mythologies) would never have thought to mention. So don't underestimate the value of the information you think is worthless! A thousand years from now they will regard you as a deluded primitive, but they will be interested in your internet traffic and your credit card records. But of course, don't forget to preserve the art too.