I would love more different kinds of items such as breeding items or other boosts, boons, or things that give you an advantage during gameplay. I find breeding challenging so maybe breeding or CP or explore items, give a random boost to a pup etc. I usually spend a lot of time intentionally exploring during these events, and I will play even more if the items in the event shop are breeding related or similar.
My second choice would be event dyes or I also specifically collect the border-type decor items. Like the vine borders or flower border or light snow overlay.