Sandwich was long invented before John Montagu, 4th Earl of Sandwich (located in south east England), an 18th century English aristocrat, lent his title to it. The guy was known to be an obsessive gambler and to avoid leaving the gambling table to take supper, he favored this portable type of food. It allowed Lord Sandwich to continue playing cards, while eating without getting his cards sticky from eating meat with his bare hands.
Trivia: Be ready for some chuckles!! To the south of Sandwich is another little town called Ham. So the road leading to the towns has sign posts reading:

Ham
Sandwich
A sign that gets stolen every now and then.
And if that did not raise a chuckle, then try this, there's yet another town called Deal nearby, so there are places where road signs read.....(you guessed it!!!)
Ham
Sandwich
Deal
Sources: http://www.answers.com/ , http://en.wikipedia.org
Image: Google Images