ACan I add sour cream to a box cake? If so, how much should I add? And do I replace the water with buttermilk? ... I just need a couple tips on how to make boxed cakes a bit more moist. Please help! Thank you in advanced (:

Why don't you try a WASC recipe?  It's a doctored box cake mix recipe.  The original is 1 bx cake mix, 1 cp flour, 1cp sugar, 1 cp sour cream, 1 1/3 cp water, 1/8 cp veg oil, 4 egg whites, 1 tsp vanilla, 1 tsp almond extract.  There are many variations to this recipe which you can find on CC under recipes.  One other note, with the new smaller size cake mixes, it is advised to use 1bx plus 1/2 cup cake mix and cut down on the sugar to 3/4 cp.    Above recipe will make 2 8" rounds.

HTH

AI'll give it a try! Thank you!