Actually now you can get Vanilla flavoured Slurpee's (I don't know if you all have them, may just be under a different name) and if you mix it up with a Coke Slurpee... you're golden! Vanilla Coke just in Slurpee format!
I was so super excited this weekend. We (some friends and I) ended up eating at this Fast Food Restaurant called Hurricane and instead of the usual soda you get you were allowed to substitute for a Slurpee or Slush. I've never experienced that before! So it was awesome!