Some terminals stay open all night, some close entirely after the last departure, and a few are genuinely comfortable. Where to find the seating that works, what to pack for a cold and brightly lit night, how to secure a bag while unconscious, and when the airline owes you a hotel instead.
Leaving the airport on a layover comes down to two questions: whether you may legally enter, and whether the timing works. A country by country breakdown including China's expanded ten day transit scheme, the UK authorisation now required of US citizens, and why US connections are the hardest of all.
Airport security is relaxed about supplements, with no quantity limit on tablets and no requirement to keep original bottles. The complications sit elsewhere: the 12 ounce powder threshold, liquid vitamins under the 3-1-1 rule, and destination countries that regulate melatonin and high dose vitamins as medicines.
