[Avoid jetlag and airsickness] Respect the local customs
Some countries, especially in the Middle East and Asia, dress more conservatively than we do. You shouldn't wear shorts or sleveless tops in these places, so ensure you have some other forms of clothing packed in your bag. It is also handy to have a long-sleeved top packed in your daypack - places like St Peters Cathedral in Rome require you to cover your arms when entering the building. You don't want to miss out on the opportunity to see such fabulous places just because you don't have the right top with you!