wow - the very thought i've been having over recent weeks - have been and da'd myself only last month and now thinking on this subject
so far i've decided to keep one copy of everything (the rest went in bin bags) and that reduced the bulk substantially but i still have a heap of literature
apart from one of the studies in the scriptures (something about armageddon ...) my oldest one is a floppy covered book from about 1920 by rutherford called 'talking with the dead' (sorry i can't be bothered to go upstairs and check the details) - it's a book i found in an old bookstore and i was given a very disapproving look by the book-study conductor (heehee - he didn't realise it was a society book - and then when he did, i think he was even more worried) ...
for the moment, these books are part of my heritage and how my life has been moulded - i can't bear to throw them away