In addition to formal evenings on longer cruises, formal attire can range from suits and cocktail dresses to formal evening gowns. No problem if you don't feel like packing anything formal - not all dining venues require formal attire! The following guidelines are followed for Formal evenings: Cruises up to 13 days: One Formal evening. There will be two formal evenings on cruises lasting between 14 and 20 days. Three formal evenings are required on cruises lasting more than 21 days.