If you want to test an object, and not have to add it in the client XMLs, put the object in addition.xml and use the tag ' ext="true" '.
If you want to add a new object to your game, put the XML in dat1.xml on the server, and a copy in the corresponding XML client sided. You can use almost any client XML, but it's better to do it the right way from the start instead of having to go back and cut/paste all of those things you added.
So in example, this potion would go in dat1.xml on the server, and since consumables are equipment, in the client it would go in the equips XML.