Engelman has one hard-and-fast rule about staying hydrated during the flight: you can never have too much moisturiser. Lawrence can appreciate that: "For my body, I use the Palmer's Cocoa Butter Formula Moisturising Lotion ($4) — it's great for feet and elbows. I also sometimes put the cocoa butter on the tips of my nostrils if they are really dry. During the summer, I switch to Aveeno lotion with SPF 15." (Dermatologists recommend applying a thin layer to the skin every hour of flight time.)