According to the Wikipedia article on sandwich, the food was named after the Earl of Sandwich. How much details exist about his first sandwich? Is there enough details to accurately recreate it?
It is said that the 4th Earl of Sandwich, John Montagu was the inventor of the Sandwich. He was also a supportor of Captain James Cook as First Lord of the Admirality approving funds for Cook's second and third expeditions into the Pacific. In return captain Cook named the Sandwich Islands( Hawaii) after him.
The story goes that The Earl was playing poker and wanted to eat meat without leaving the Poker Table. So he asked his servants to put the meat between two slices of bread. The poker table idea may not be entirely accurate. It may or may not have been made up by people who were not friends of his. Another story says he may have been working and didn't want to leave his desk.
Many of the articles I read simply say he put "meat " between the bread. However, this article says it was Salted beef-(Corned beef) which fits in with the era. Salt was used as a preservative.
I hope this helps.