It starts with a strategically packed cooler.
1. The day before the party, bring your cooler inside (e.g., out of the garage) to let it cool down. Fill empty water bottles or milk cartons with water and freeze overnight to create slow-melting ice blocks.
2. The day of, pack the cooler tightly, alternating the ice blocks, ice packs, and loose ice (the fewer open spaces, the colder the cooler will be). Nestle a sheet tray of unmolded pops in the center and pack ice around it. Or fill freezer bags with unmolded pops and stash between layers of ice.
3. Set the cooler in a shady spot, close the lid, and cover with a towel. Pops will stay frozen for about one hour.