I usually bring my NaNavigator because it has ALL of my tools in it. I think you're supposed to be able to put an album in there, too, but it's too full!
As for what to bring, it depends on where the crop is being held. Is it at a store or someone's house? If it's at an LSS (local scrapbook store ) then you might not need too many tools as they usually have quite a selection; if it's at someone's house, you may want to plan out your layouts beforehand to determine which tools to take with you. or call the hostess to see what she has that you can use.