Travelling with only hand luggage? Pop a couple of 75ml bottles of Soltan Once 8 Hour Sun Protection Moisturising Suncare Spray SPF30 (£10) in your bag. Though none of these "once a day" formulas truly give you protection for a whole day (especially if you're going to be swimming or sweating), you can apply slightly less frequently, allowing you to eke out a small bottle for as long as possible. I tested this out in the Caribbean and got through a whole day sunburn-free with only a couple of top-ups to my fair skin.