You can throw excessive amounts of items you will not need any soon in next months/years.
We will not create extra big stack sizes for items just for 1 player. We increase it only for where it is clearly worth or never increased before.
You can also place 1000 chests of 40 slots each in house, use house servant storage, whole bank, whole bag, put skins into magic wardrobe, fill guild bank, use other characters in same account, sell not needed items. That is plenty of possibilities.
Greetings