Or don't eat the pizza? Unless you are trying to stick to a very restrictive diet, a slice of pizza isn't going to ruin your health. Keep going to gym, eating healthy, and either eat before the event or just stick to one slice of cheese pizza if you must munch with everyone else. It would be nice if there were other options for events like that but there really isn't a healthy, cheap alternative to pizza that fits the same role and has the same universal appeal.