Pack a carry-on around the journey you actually have
A useful packing list begins with the trip, not a universal set of essentials. A short work visit, a train holiday and a weekend outdoors ask different things of the same bag. Start by writing down the actual days.

Map the changes of setting
List the places where you will need different clothes or equipment: travel, work, sleep and the activities you have planned. Look for items that can serve more than one setting without being uncomfortable in either. Check your carrier’s current baggage rules directly before packing; a bag described as cabin size is not accepted everywhere.
Make the first hour easy
Keep the documents and small items you need on arrival in an accessible pocket. A compact pouch can prevent cables and adapters from disappearing into the main compartment. Put anything subject to security or transport rules where it can be removed easily, and check those rules for the route you are taking rather than assuming every airport is the same.
Leave a little empty space
Pack the bag fully, close it and carry it around the room. Can you reach the essentials without unpacking everything? Can you lift it comfortably? Remove duplicate items before searching for a bigger organiser. The best packing system is the one that still works at the end of the journey when laundry and hurried departures have disrupted your careful arrangement.