"The family of the Earls of Sandwich has no real connection to the town itself, only the title. The 1st Earl, Edward Montagu, originally intended to take the title of the Earl of Portsmouth - this may have been changed as a compliment to the town of Sandwich, because the fleet he was commanding in 1660 was lying off Sandwich, before it sailed to bring back Charles II to England."
http://www.open-sandwich.co.uk/town_history/sandwich_origin.htm
The town clearly goes for open sandwiches, not the closed ones you buy in Tesco's.