First, make ice cubes out of thickened fluid (whether that’s water or milk or whatever you’re serving). The bigger they are, and the less surface area they have, they longer they’ll last. I used these silicone popsicle molds.
In the morning I would take one out of the freezer and let it sit while I made breakfast/lunch. Then it was easy enough to twist the silicone and pop a giant thickened ice cube into a Contigo insulated bottle.
Then add your fluid.