[Kragenwar]

I don't know if you did as Digitial Utopia suggested and declared Data in your satchel class as self.Data (since you only posted your main and didnt repost your Satchel class). But if you did, then when saving your data variable from your main you may need to go

Turbine.PluginData.Save( Turbine.DataScope.Character, "Satchel", SatchelWindow.Data );

Alternatively you could also put the save line in the code where you write the position to data

----SAVE WINDOW POSITION----
	self.PositionChanged=function(sender,args)
		self.Data.x,self.Data.y=self:GetPosition()
		Turbine.PluginData.Save( Turbine.DataScope.Character, "Satchel", self.Data );
	end

I haven't played with the unload code Digital Utopia posted, but I am going to take a guess that maybe your call to save needs to come before UnloadPlugin(); Just a guess tho

Plugins[pluginName].Unload = function(self,sender,args)
       Turbine.PluginData.Save( Turbine.DataScope.Character, "Satchel", SatchelWindow.Data );			
       UnloadPlugin();
end

Also I noticed in your class code you posted earlier you also allow changing of size, which means you might want to save the size as well.