I wouldn't let them sit. Besides settleing out, I think the protein starts to degrade....

MAX MUSCLE.... www.maxmuscle.com make awesome ultra filtered protein powders. I do exactly what Dumbells said. I put a scoop in the shaker cup they give you. I carry that and a bottle of water where ever I am going. Then when I need it, I pour in the water, shake and voila! They are very light tasting and thin, so they are easy to down if in a hurry. They are all natural, with no fillers, gums, etc....

And the best part is they DON'T CLUMP. I hate drinking a shake with clumps... these don't clump up... water or milk...