Vanilla and coke seems like a good combination to me, although it may just sweeten the coke up a bit more.. and it is pretty sweet already. The rum is a good counterpart, because it adds a bit of the alcohol taste. I would not recommend driving your car while using the rum flavor as it will probably make it seem like you were drinkin a bit while driving if you get pulled over.. and I would love to see the first person trying to explain that it is his/her smoke juice that is producing the scent! hahah..
My current favorite flavor combination is Strawberry & Banana.. mmm. Great combo. That, and Peach+Orange+Mango. That combo is just wow.