Summarize:

While you may feel like flying is a special occasion, don't dress up to your international flight. Flights overseas are long, and you'll want to wear loose, comfortable clothes. If your flight is especially long, consider packing a pair of sweats for your flight in your carry-on. Change back into your original clothes for the landing. Some airports offer long-term parking rates for your car while you're away. Call or email about the long-term car storage options and the costs of each choice. If car storage isn't an affordable option for you, use a shuttle service, hire a taxi, or ask a friend/family member to drive you there. Check in for your flight as early as possible to go through security and board on time. You'll also have time to use the bathroom or grab something to eat before you depart. While you're waiting for your flight, bring something to relieve boredom: keep a book, journal, or game in your carry-on to entertain you while waiting. Dehydration is a common problem on long flights, which can lead to exhaustion or irritability. Buy a large water bottle to fill up before you board the flight so you can take it in your carry-on. Avoid drinking alcohol or caffeine before and during your flight, as both can lead to dehydration. Most nations require you to mark on an official form what goods you bring with you to their country. Which items you must declare depends on the country. You will likely receive your customs form at the airport and during the flight. Fill it out while on the plane so you are prepared for landing.  Some countries require a customs form for each person traveling while others require one per family. Check beforehand to know which forms you must fill out. Most countries require declaration of: alcoholic drinks, tobacco, animals, seeds, soils, medication, and animal products. International flights involve crossing time zones and long, uncomfortable plane rides. Both can disrupt your sleep schedule. Bring a sleeping mask and earplugs with you, and consider taking an over-the-counter sleep aid to help you adjust to the new time zone.
Wear comfortable clothing to your flight. Check with your airport about car parking rules for international flights. Arrive at the airport two to three hours before your flight. Stay hydrated. Declare your items for customs. Prepare for jet lag.