On top the hub's first building are several items. Collect the following in order to gain an Invincibility Combo - Cake, Hammer, Earth, Apple, Tap. Note that this only lasts for one level, so you'll have to return and collect the items again for multiple levels.
On the far right in the hub (the lower side building) are several items dotted around on the ledges. Collect the following in order to refill your power batteries - Penguin, Oil Can, Wine Glass, Earth and Racket - spelling POWER.
Around hub's first building on the ledges are several items. Collect the following in order to gain an Unlimited Lives Combo - Lips, Ice Cream, Violin, Earth, Snowman - spelling LIVES.