i am covering an event for my former school, it would be prom night

what i would like to know is what should i get for the event.

i am using a 400D with kit lens and i think the following is needed

85mm F1.8
and probably a wide angle zoom(any recommendations?)

what do you think?
advie would be appreciated, really want to make it good as its my first time shooting and presenting my works to a paying client.(not trying to imply that these equipment would make gvie me better photos!)

thanks in advance!