In short we don't, at least not intentionally.
Just like in the past but on a much grander scale it will be our trash that provides the least corrupted record of our society. I believe it was a Futurama episode that joked about the AOL CD ROM mountain which would probably be dwarfed by the K-Cup one now.
If I had to come up with an method to provide a more secure way to store our history and pass it on to future generations...and had unlimited funds. I would land a multiband and frequency transmitter on Halley's Comet set to broadcast every 80 years or so when it comes into range of the earth.