In Hello Kitty Island Adventure, you'll eventually unlock the ability to brew potions. Drinking these will give you temporary buffs, so they're good to have. In order to do so, you'll need to start and complete the story quest "Potion Hunt: The Opening," which becomes available after you've befriended and leveled up Kuromi. Depending on how much you like exploring the islands of Island Adventure, potions may be one of the first things you should unlock to make your wall climbing and diving easier.