I have this macro copied from somewhere, it will trade items.
I will assume that on you alt you have your main set as focus. Else, replace "focus" with some other unitid (you can use target and prepend a /target character, but it might be subject to lag).

And replace Fish Oil with the name of what you wish to trade (Master Healthstone?).

/run for i=0,4 do for x=1,GetContainerNumSlots(i) do y=GetContainerItemLink(i,x) if y then if GetItemInfo(y)=="Fish Oil" then PickupContainerItem(i,x); DropItemOnUnit("focus"); return; end end end end