If you have a drop down menu component, you can put it as a child for rich:toolBar and that is it.
The question is only - do you have such comportment?
Richfaces library has no menu component yet, so you need to use any other third-party library.
rich:menu is on the Richfaces 3.1.0 Roadmap
Would you suggest using something like <t:jscookMenu /> ?
Yes, but I have no personal preferences to suggest something particular. So, it is up to you.