Rear wheel, cassette, chain, rear dérailleur, shift lever. I just put all that in the Chainreaction basket and applied voucher UK15 and it came to £128.95, or you could get nicer kit second hand. Your bike also needs a front brake and lever, but that's nothing to do with converting to geared. Might also need a chainring if you're running ⅛" at the moment.
i keep meaning to buy one for the front
thanks for the advice