Enma - In Part 1, he's already shown to be a Kage-level summon. What if he was shown during Part 2? If you're ever outnumbered, he can take out a few at least before he gets mad and de-summons himself.
Gamabunta - Obviously. Flattened Kurama when Kurama had all of his chakra (only half of Kurama's chakra is sealed into Naruto yet Kurama's TBB still = 5 combined TBB's).
Katsuyu - Ultimate back-up for any Senju/Uzumaki who gets overconfident and may get injured. Unless you get beheaded, you ain't dying.