I agree with Dzug 100%, there is no need to keep them at all.
It can, however, be useful to retain one bank statement or bill from each year as 'proof of residency', in the event of an electoral roll issue that means having to prove you lived at your address within the last 6 years. This may occur if you apply for finance for example.
My advice is to invest in a good shredder and dispose of your personal documents securely, as identity fraud is largescale now and it is not uncommon for documents to be stolen from unsuspecting peopes dustbins!
Good luck