One of the most neglected but most important parts of the gas setup, the regulator is a cheap and cheerful device which provides smooth and stable gas flow.
Worth keeping as a spare for when you are stuck in the middle of a field (and hungry!) these items are surprisingly cheap but easy to fit, usually just requiring a flat bladed screwdriver to tighten the jubilee clips.
CamperAuctions top tip:
Don't forget to buy hoses and jubilee clips or a 'bundled' offer unless your current hoses are not too old or perished. Check the condition of regulators and hoses often as they can suffer damage, particularly at the ends under the jubilee clips. Cutting off an inch may help if it is just a little split at the ends, but make sure you have enough hose to reach your appliance comfortably and that the regulator hose is not perished or damaged.