Just from my experience with several long term trips. For me, in any case, setting out on such a long ourney is a chance to declutter and that can be very liberating!
I recommend everyone to start very early to sort everything out, because I know from my own experience that this can take longer than initially thought! In addition, the sorting out and thus the process of letting go can be a great time to prepare for the journey and to slowly approach the new.
So, start early and work your way through consistently:
Give Away
This is a good option for things with which we can make others happy. Be it something that we have several times anyway or things that are no longer in a condition that we want to sell them, but which are still too good to throw away. You can make friends and relatives or people who do not have it so well happy.
Donate
For a good cause. If you want to donate items, you have a wide choice of different institutions and projects. I have had consistently positive experiences here with social department stores, where donated goods - often by the long-term unemployed - are refurbished and sold at affordable prices to those in need, and other social institutions and projects. In this area, there are also numerous projects that combine our hobby offroading and overlanding with the good.
Consume
Once it is clear that you are going on a big trip, consistently do not buy anything new that is not absolutely necessary, but consume what is already there.
Sell
There are a variety of possibilities here. Depending on the item, online platforms, 2nd hand stores that take goods on commission, flea markets, maybe even a garage flea market, travel and overlanding meetings, forums, classified ads, search-offer notices and much more are suitable. A great side effect: selling fills the travel fund.
Storage and Shelter
And what happens to the things that you would like to keep? Often it is personal things, things with sentimental value or others.
You are not always lucky enough to have friends or relatives who have a storage facility. Then the already mentioned self-storage companies offer here a simple and flexible possibility.