Make Kid join the party.*MISSABLE*
To have Kid join the party, you must have talked to him in Junk City prior to the soldiers coming to town. He will be working on a snowman for the earlier parts of the game while you work on lighting the beacons and you can talk to him at any point during those events. Once the soldiers come to town he will be gone, then after you complete the Ice Lair, so long as you talked to him in the first part of the game, he will waiting in that same spot in Junk City to speak with again. Do so and he will join you.