Two styles of thin rubber Rostrevor wristbands. Black with red writing "Rostrevor Forever" or black with green writing "I 'shamrock' Rostrevor".  You may need one of each. :) Cheap and cheerful souvenir exclusive to Good Craic Gifts.
Good Craic stocks a wide range of Irish souvenirs including many items you may not see elsewhere. I cherry pick the very coolest items from the various suppliers. The shop is eclectic and fun and definitely worth a visit if you are in the Mourne area. If a product doesn’t exist yet I might just create it myself as I’ve done with these.