Biff has one heck of a newspaper collection:
Biff shut himself in his room downstairs. This was the place where he kept his files. [...] Huge stacks of newspapers rose up to the ceiling. A homemade filing case covered one wall. [...] Because of the piles of newspaper it was impossible to take more than two steps in any direction. (2.8.84)
This guy could open up his very own library at this rate. But if he has to hoard something, at least it's something of historical value. The newspapers act as another comment on theme of memory and the role of world events in the novel. Biff has literally walled himself in with his memories and historical events to such an extent that he can barely move around in his own "room," which, as with Mick, acts as a metaphor for Biff's mind.
Like the events they contain, the newspapers are also separated from people, stored in a back room. But their presence is significant, and they symbolize how memory and current events linger on the outer edges of people's lives. What other symbols help us see that?