Magnetic swipe room keys are standard issue at newer hotels, but unlike old-fashioned keys they don't have a room number on them. Good for security, not so good if you're forgetful. Rather than carrying around the little cardboard wallet the key comes in, snap a photograph of your door on your phone.
That point is highlighted in the slightly cheesy travel tips video featured above, which includes Aussie tennis great Pat Rafter. We've mentioned the usefulness of photographing things you need to remember when travelling before, and it's a point worth reinforcing.
Perversely, one of the easiest ways to ruin a magnetic swipe key is to store it in the same pocket as your phone. I usually store mine in my wallet.