Pieces of plastic that came with my bike, what are these?
These are cable guide parts.  From the looks of it, you have:


2 Housing shims, used to secure hydraulic lines or brake housing in the braze-ons of the frame, or for securing the housing at the point it enters the frame in the case of internal housing.
1 Headset adjustment bolt button, used to keep water out of the bolt in the center of your headset cap, or to hide the bolt.
2 Hydraulic line clips, used to secure hydraulic lines or cable housing on a particular type of housing guide on the outside of a frame or the back of a suspension fork.


Many frames come with extras of these parts, so it may be that you have no need for them at this time.  Or you might, if the LBS did a poor job of assembly. No way for us to know without seeing your bike.