Try Peach Black Tea Lemonade and the Strawberry Acai Refresher. Both give you as much caffeine as coffee but hydrates you more. If you can, try to cut back one cup worth of coffee a day until the test so that's more effective come test day.
You'd be better off drinking 2 black coffees IMHO. Red bull doesn't have that much caffeine and I'm not sure how helpful its other stimulant ingredients are. and unless you're drinking sugar-free then there could be a sugar crash