Apps/music would be my first suggestion. Convenience of renting iTunes movies is nice, but at 5.99 just redbox 3-4 movies and save the iTunes credit for stuff that will last. Besides, Amazon's rentals are 48 hours if you want instant streaming.
Find something you're interested in. Music? Mainstage is right there in that budget-- best bang for buck imo of almost anything in the app store.
Video/effects? Motion 5 or one of the animation apps.
Really push yourself to learn something-- 30 bucks and your mac and you could develop a very useful hobby or even a new job skill.