No matter how much we nail it home to you guys, you won't always come prepared to every situation with a full line of sun protection products. Going to the beach is one thing, but what about those days where you unexpectedly spend way more time outdoors than you originally planned? It may not necessarily be easy to plan for every situation, but there are fall-back solutions you can implement if you're ever stuck in a sunscreen draw.
According to StyleList.com, many SPF-containing chapsticks can serve as a great sunscreen substitute when you're low on the real stuff. This is an especially useful tool for reinforcing areas that tend to get a lot of sun exposure, such as your forehead, nose, ears and cheekbones.
That being said, you don't need to get caught unawares as long as you practice good planning. Prepare a sunscreen kit containing one or two different types of SPF30 sunscreen as well as one especially designed for the face and an SPF-containing chapstick. If you keep your kit in your car (or your totebag in the summer, to avoid leaving it in high-temperature environments), you'll significantly increase your chances of always being prepared.