Keep the most popular at the time. Pulp. The weird fan fic you wrote when you were 14, memes. The things that actual people enjoy, there is a lot that someone 1000 years from now can learn reading your weird embarrasing fan fiction and diary.
The rich and powerful are going to preserve all their crap just fine, the normal everyday doesn't seem to get high priority for preservation.
Czech Sphinx? Because it's a riddle how he was allowed to aquire royal mail or because he is going to squeeze it dry?