Most people can navigate rooms in their house in pitch dark without a second thought, or a flashlight. We circumnavigate obstacles in our own homes, like furniture and pet food bowls, without collision or injury because we all know where things are in a familiar environment.
Just like knowing the layout of your house allows you to navigate it in the dark, knowing where things are in the aircraft allows you to get anything you need during the flight, at any time, without taking your eyes (or mind) off of the task at hand: flying the airplane. This is called flight deck management.
Start by thinking about what you need for a flight. Headset, of course—and charts or an electronic flight bag. What else you bring depends on you and the flight’s purpose. For example, you may want to pack an E6B, foggles, flashlight, water bottle, snacks, personal locator beacon, or any of the other thousand-plus things from your favorite pilot supply website. But whatever it is you bring, each and every object should have its place in your flight bag.
When you arrive at the aircraft, think first about where your bag should go, what items should come out of it for easy access, and where to put them. After your personal gear is managed, think about checklist management: where to keep your checklists—the routine (normal operations) checklist(s), and the emergency checklist in case you need to grab it quickly. As you progress to larger aircraft, those checklists grow in size and number, and you will appreciate the good habits you developed, always keeping things organized.
There’s no right or wrong way to do any of this, so long as you develop a system that works for you and that you’ll stick with. That way, when your active noise reduction headset batteries give up the ghost on your solo cross-country, you'll know exactly where your spares are.