On 7 night voyages or longer, formal night is typically on the first full sea day, which isn't always the second night. Additionally they hold the Captain's Reception, when there is a chance to meet the captain and get a photo with him. This is one of our favorites to buy as the date and ship info are printed on the photo.
As stated there are lots of photo ops on deck three and 4 with nice back drops. There will also be severs circulating with free drinks alcoholic and non.
Quick edit, the Captain's Reception happens twice, approximately 5:15 and 7:15 to accommodate both seatings.