The items currently are small figure cases for all mobs in the vanilla game and their variations such as: sheep, shulkers (with all 16 colors) villagers (with all six variants) zombies, cats, rabbits, parrots and many more.
The main goal of the mod is to move the player out into their world to find some of these items, they don't change anything about gameplay but they can give a sense of satisfaction when you finally finish a collection. Plus some of the items are very rare and can be really exciting when you find one of them, and even the ones that are common are amazing to find.
There are still some things that are in the works, such as some crafting and ways to make getting the items easier and more fun, but those are features for the future, hopefully near future.
The screenshots were taken using Chocapic13's shaders.