It depends on what you want and what you're serving at your reception. Our brunch reception was a buffet, so we took food off of the buffet and moved it to the pre-reception at no extra cost. We had fruit and pastries at our pre-reception along with a non-alcoholic bar (we had a dry reception). It gave people something to munch on until we arrived and also saved us a ton of money.
Carrie (aka Lurkyloo) can give you all of the details. It was thanks to her book that I knew we could do that to begin with!