Freeze the tube itself, then back it with a big gel pack.

The easiest way to keep a frozen yogurt tube or smoothie cold until snack time is to freeze it solid and then pack it directly against a large gel ice pack in an insulated lunchbox.

The tube is already a cold thing, so it works as its own little ice pack. But it’s not enough alone. By 10am it’s soup. The trick is pairing it with a proper companion: a thick gel ice pack. The cheap thin blue bricks that come in meal-kit deliveries warm up way too fast. Get the flexible gel packs — the ones that stay bendy even after hours in your freezer. They hold cold much longer, and the bigger the better. Lay it flat against the yogurt tube, not just tossed somewhere in the bag.

Also, the lunchbox itself matters. A flimsy nylon bag loses cold fast. Use one with thick insulation, and make sure the zipper is closed properly. If you’re carrying a smoothie in a thermos instead, freeze the smoothie inside the thermos overnight, then drop a small gel pack on top before sealing. That keeps it drinkable-thick instead of watery.

Do that and it’ll still be frozen (or at least very slushy) by snack time. That’s the difference between a smoothie and a sad purple puddle.