Fumio's answer is good for "busy days make you hungry", but if you want to say "this busy day made me hungry" it would be something like "今日の忙しさでお腹がすいた". You shouldn't trust me though, I've never heard someone say that so I don't know if it's right. (Fumioさん、助けてくれ~)
Anyway, did you get hungry by just being busy or was it really because you were busy and didn't have time to eat, or because you did lots of stuff and got exhausted and hungry?
Saying the latter ones would be easier because they're way less abstract. (and make more sense IMO)