The best types of foods are the ones that digest best... some guys can handle greasy foods or shitload style stuff no problem, others need to stick to the kind of carbs they have been using all prep.
I personally don't like to leave anything to chance... if I haven't been eating something all prep, I am not going to eat it the day of a show (if the ingredients of a snack bar are things I normally eat, I will eat them, as they are things I have eaten all prep - so I carefully check ingredients)... I also have a very bad GI system, so I need to be more careful... but liek i said, some guys may not have eaten garbage for 16 weeks and then down fries, pancakes, doughnuts... and be fine.. what is best is to make sure you are ready for your show (condition wise) a few weeks early and then do a trial run... This way you take the guesswork out of the actual contest day.