One nice luxury, that sometimes can be a necessity, is access to an airport lounge. I have had some unexpected layovers and flight delays that became much more tolerable because I had access to a lounge. Fortunately, as an Army reserve officer, I have the added benefit of the USO. In fact, there are some USO airport facilities that can rival an airline lounge. Of course, USO airport facilities are only for military personnel and veterans, but I definitely recommend you check them out if you qualify.
For the airline lounge, which can be an expensive membership proposition, there are several ways to handle it. Some offer pay per use access, and that can be a good arrangement if you have a long layover. I will be traveling to the middle east later this year and will have a long layover at an airport at which I do not have lounge access. In this situation, I plan to pay for day use at an Air France lounge (which includes the use of showers). For me, those shower facilities, along with the food and drink options, make it well worth the day use fee.
Some credit cards come with airline lounge memberships, and, if you travel extensively, they may be well worth the annual expense. These cards, such as the Ritz Carlton Card, charge around $450 per year but they also come with additional perks such as Global Entry application fee reimbursement, travel credits, hotel credits, and other worthwhile perks. If you do not want to pay the high annual fee of one of these cards, you can opt for other cards, such as the United Rewards Card, which comes with two day passes each year.