Rabbits are just another example of a cool but totally unnecessary detail that developers decided to add to Skyrim. Who doesn't love cheese? Even in the world of Skyrim, it makes for one of the greatest delicacies across all of Tamriel: the famous Elsweyr Fondue.
The Dragonborn can actually just walk into water and catch fish with their bare hands, which seems a bit too easy for someone who might not be a master fisherman. Fishing is one of those hunting methods that see little use in Skyrim due to being quite counter-intuitive. It is of course acquired when killing a cow, and is the key ingredient to one of the heartiest stews in all of Skyrim: the beef stew. For the ultimate food boost, there's no doubt that beef is the answer to all questions.
Should the player come across venison, they should never, under any circumstances, make venison chop out of it when wanting to maximize benefit from their cooking.