Jet lag always seems to get the best of me when I travel. I’ve tried prescription sleeping pills, well-timed cups of coffee, and even gradually adjusting my sleep schedule in the days leading up to a trip. But I hadn’t used melatonin to help regulate my sleep cycle, so when Sundown Naturals Adult Melatonin Gummies ($4; amazon.com) landed on my desk a few days before a recent trip to Europe, it seemed like fate. I…