Well, here is a cost saving tip, especially if you are taking classes.
Whenever, I am unsure if a products is still good (i.e., eggs, milk), I will use those to create my class cake and/or create dummy cakes. It saves you from wasting your good supplies when you just want to practice. You HAVE to make sure that you throw the cake away once you are finished.
I am a stickler about dates/contamination so I'm afraid to use anything after the printed date.