The more ice cream you add, the bigger your shake will be. Vanilla ice cream is usually used as a base to add candy flavors to, but any type of ice cream flavor works just fine.
Depending on how think you want you shake, you can add more milk to make your shake thinner (1/2 cup of milk), or less milk to make it thicker (1/4 cup of milk).
It doesn’t matter what kind of bag you use, but the main point is that you want your candy to be confined somewhere where you can smash it collectively and keep the candy together. The more translucent the bag material is, the better you can see portions of the candy that are already smashed, or still need to be smashed. Be sure to keep a lookout for holes in the bag created by smashing the candy. Smashing the candy helps with blending the candy into the ShakeAway, and also helps reduce damage to the blender’s blades.
Be sure to put on the top of the blender, so you don’t splash milk and ice cream everywhere.
A general rule of thumb is, blend the mixture less to have a thicker ShakeAway, or blend it more to have a thinner, smoother ShakeAway.