I have done 3 long succesful MCs 40/28/21 and have premixed on all of them.
I have a collapsable cooler and some of those reusable blue ice packs. I would make 3 qts in the morning and divide then into 3 Nalgene 1 qt bottles with sports caps and take them in my cooler wherever I went and sipped on the lemonade all day long.
Here's the recipe for making 3 qts (9 drinks)
18 tbs = lemon 9 oz
18 tbs syrup = 9 oz