Order what you would normally order and don't worry about the mess or what your date might think. Too many people do these little changes to their lives when dating that ends up creating a false person. Don't ever change yourself for your date. You are just setting yourself up for an uncomfortable situation when you go back to 'normal' and things surprisingly don't work out.
I agree with rban68. Don't play silly games and present yourself as someone you are not. If he accepts you after watching you eat a gooey pastry and licking your fingers, you are in!!!!
Messy can be really sexy...get what you want ;)
just be yourself