Since it's summer time and hot, I like this for a daytime/outside drink:
"Tropical Punch" flavored whey protein (I use Optimun Nutrition)
Add 2 scoops to 12 oz. water and blend in blender
As it's blending add in a cup or two of frozen mixed berries
You can add some flax or olive oil to the blend. It imparts no tast, and it adds calories.
This makes a very light refreshing drink that's perfect for the summertime. You will need to keep these shakes iced down (in a cooler) if they are going to be out in the heat.