Pizza. I ate a lot of pizza. I walked around too, but only because I needed something to do between bouts of hunger which I could satisfy with pizza.
I found it surprising in retrospect that I didn't take a single SLR photo of pizza. Then I remembered the animal-like voraciousness that overwhelmed my senses when those pizzas slid onto the table and dispelled any restraint.
Besides, Naples isn't a city of polite restraint. It's a down and dirty city that trades tourist glamour for good food and authentic street strolling. You can even spend the day in Pompeii and make it back by dinner, when you'll probably have another pizza.