Customs at your destination will most likely be perfunctory. They are really not interested in you. When you return home, you will be asked to fill out a form on which you specify if you have anything to declare. There are many disallowed items, most for agricultural protection, such as plant materials and certain foodstuffs. If it's night time at your destination while you're on the airplane, try to sleep, or at least rest.
Many frequent travelers take along inflatable pillows, eyeshades, and earplugs.
Remember that the free drinks and movie are surly not as interesting as your destination will be - get the rest you need on the plane. Style comes second to comfort for most people. If you're heading eastward, do not go to bed until evening, except possibly for a very short nap. Experts recommend going outside, in sunshine if possible, as an aid to resetting your internal clock. If you do get out of phase with the local time, you may ruin your vacation by being wide awake nights and sleepy during the day.