The packing list has two main uses.
You can consider the needs of your next trip and list all the special items that the route, mode of transport, destination and activities require. This can then be refined in the light of the availability of shopping and services.
2. Act as a Checklist
When you are packing to move to the next destination you can use the packing list as a checklist to ensure that everything you brought with you has been packed, and that you have not left anything in the bathroom, the bedside drawers, or in the hotel safe.
Obviously, for use as a checklist you should add everything you acquire during the journey, so that you take all your new belongings with you as you travel to the next destination.
You can keep your lists when you have returned home and use them for subsequent journeys, along with any items that you feel are now essential. It also serves as a basis to say “I did not use these items, and they are not worthwhile taking along with me next time”.
Depending on the customs regulations in your home country you can either have the list stamped by a customs official before exit, or use it to complete a formal declaration for submission, that will serve as proof that you took specified valuables out of the country with you. This will obviate any problems upon re-entry with customs attempting to charge you duty on the goods you took out with you.
Rather than just dumping everything into a universal list, you may find it works best to list items within categories, such as: Clothes, Toiletries, Food, Medical, Special-interests, General. Add and delete categories as you see fit.
Test your list with other travellers, your travelling companions, and those that may have expertise in your mode of transport, destination or destination activities. You can also consolidate lists if you are travelling in a group, to avoid duplicates. For instance, perhaps one of you agrees to take a slightly more hefty first-aid kit, another one may take a water purification kit and a third member of the group might take a ground-sheet … you get the concept. If it is done right then everyone carries a little less than they would have if each person had planned independently.