The 2 most important things you need to take to your driving test are the provisional licence and paper counterpart - without both of these, you won't be allowed to take a driving test.
If you have lost either, you will need to apply for a duplicate through the DVLA as soon as possible (a duplicate will cost £20).
The quickest way to apply for a duplicate is to ring the DVLA duplicate service on 0300 790 6801 (they will accept card payment - Visa, Eurocard, Mastercard, Solo, Electron and Maestro).
You could also apply for a duplicate online or by completing and sending the Form D1 (available at the Post Office) to the DVLA.