You can mix it in whatever you want, just keep in mind soda would probably taste discusting (to me) and be full of crappy sugar.
GNC is overpriced, and supposedly of low quality - I would rather order it online. I really like Optimum Nutritions 10 pound bags, in chocolate, vanilla is nice too. Chocolate tastes like Ovaltine though, its the best tasting protein I've had so far, hands down.
Good tasting in warm water or good in milk. Should cost you about $45 for a 10 pound bag, GNC should be about double that last time I set foot in there for a supplement purchase (not protein, thats for sure).