A smaller cockpit is preferred by some because it is considered more watertight. Deck lines that run along the edges of the deck from the bow to the stern are important safety equipment. Bungies that cross the deck in front of and behind the cockpit are handy for stowing gear where it is easy to reach. Some paddlers prefer to have built-in compasses and pumps in their boats. Tow systems may be necessary for aiding other paddlers.
Different boats come with different kinds of deck rigging.
Anything it doesn't have that you want you will have to add. Overnight trips do not need as large a boat as week-long outings. If that's you, you need a bigger boat. A bigger boat will also be easier to paddle in bigger seas than a smaller boat. Single kayaks provide greater maneuverablity than doubles.