Foam! Foam! Foam! If you have not played around with this amazing material here's your chance. Foam is so incredibly affordable and you can make just about anything with it. It would take me days to even begin to scratch the surface of the tutorials dedicated to foam craft, but I feel you're cheating yourself if you don't give it a try at some point. If you are looking for some solid instruction, I can't recommend Punished Props highly enough. Their Foamsmith Trilogy is my go to, and their tutorials are top notch.
My first "Wow!" foam moment was with the Dracula Untold armor by Real Illusion Creations. I had no idea that it was possible to make something so detailed and promised myself that I'd learn how to utilize this material at some point.
My project for today, a class book for the Siren from Bordlerlands 2, is far simpler, though. But here are a ton of other foam options if something else catches your fancy.