[@Crimson Flame]

I went ahead and gave it a bit more thought. There will be cafés IC where players will be able to buy Pokéblocks, Poffins & drinks (no Malasadas) should they choose to. 

That being said, for your Key Item you could take either a Portable Berry Blender or a Poffin EZ-Bake Oven. Both appliances would be roughly as cumbersome as any other Key Item (eg. bicycle, fishing rod, portable Berry pot, etc), and either will serve to prepare and store your treat of choice. 

Please don’t worry about needing a specific storage for them (such as the Pokéblocks Case).