Art is hard. While your first choice should be finding a teammate who is artistic, we don't all have those connections. Luckily, there are free assets out there in the public domain or under the Creative Commons license. As we find good resources, we'll post them here for everyone to see. If you find any good resources, let us know at firstname.lastname@example.org and we'll post them here!
Disclaimer: Free art doesn't mean good art. You should definitely look to find an artistic teammate before you look here.
Huge libarary of spritesheets for almost any type of game. Very impressive. The Common Public license it uses is very similar to public domain, but make sure you read it to fully understand it.
This is a huge zip of a bunch of fantasy-styled sprites. The animation isn't perfect and nothing is in spritesheet form, but still cool.
Almost entirely classical music, but it's all good and in the public domain
There is a huge variety of surprisingly high-quality music here. Just be careful - nearly every song carries with it a non-commercial clause, which means you probably don't want to use any songs on here if you plan on selling your game after the competition (unless you work out a deal with the author).
A lot of good stuff. The license terms vary by user, so make sure you're following all of the restrictions.