A few additional thoughts to add to the good list that others have already prepared:
- You have a favourite seat or seats on each variant of each aircraft on each of your regular airlines
- You can somehow manage to squeeze in five days' worth of business clothes, your gym attire, a coat and scarf into a carry-on bag
- You get irritated when people in front of you in the security queue aren't already fully prepared by the time they reach the x-ray machine and/or when they take more than a few seconds to deal with their coats, jackets, shoes, belt, laptops and liquids / aerosols / gels
- As you look at the menu, you realise it's exactly the same as when you last flew the same route
- As you switch on the IFE, you realise that nothing new has been added since the last time you flew
- As you wait for the airbridge to attach after an overnight / long-haul flight, it's you who needs to tell the cabin crew that "...it's usually L2 at this airport..."