I can definitely recommend that Leo prepare some stuff, though; his items pack a fair bit more oomph than Kitty's. We aren't exactly hurting for versatility or firepower given that the group is composed of primary magic-users, but it couldn't hurt to have some panic buttons or prepared rituals. We have plenty of concealment, movement, and combat applications in our on-the-spot magic, so some more niche or obscure effects are most interesting.
Some kind of counterspell potion could help, given that we're likely to face down fellow magic-users here - just dump in a load of shifts, lob it and hope it works. Saves an assessment action and doesn't require a roll to control while bringing enough power to dispel most evocations and some thaumaturgies.
Potions that give bonuses to specific rolls are precedented in Red Court Antivenom and the True Seeing Ointment - just a bonus equal to the potion's strength (i.e. a huge one) to a single specific kind of roll. I'm sure there's some area we could find a use for this in.
Painkiller or even healing potions might be useful as well (see the Stimulant potion and Elaine's Reiki Healing thaumaturgic spell - the latter is expensive when applied to higher-valued consequences), though the latter is less necessary when two thirds of the party have Inhuman Recovery.
Finally, consider effects that our elements don't cover - Kitty's element is conceptually Fire, but the mechanics of it are closer to Spirit in the Western system, Leo's is Earth, and Phil's is Air, so we're basically missing Water and about 0.5 parts fire. That's not a whole lot we're missing out on, though.
