On a persistent server, leave any container (clothing, backpack, tent, etc) on the ground with some items in it.
Wait for the server to restart.
Drag any of the items in that container onto the ground, put some back into the original container or on the character's inventory. Those items will be deleted in 30 minutes.
The only way to avoid the item deletion is by logging out and back in - items in the characters inventory will not be deleted.