This USB adaptor plugs into the cigarette lighter of your car, allowing you to charge up to four devices at the one time. That means him and her can charge phones simultaneously, avoiding the inevitable “mine has even less battery than yours” argument, with two ports left over for good measure.
RRP £17.99. Now £6.99 delivered from Amazon. If you can't wait to get your hands on the adaptor, you can pay a bit extra and upgrade to first class or express delivery.
(Thanks to ramnee at HUKD)