This is the inside of the menu I posted last week. I don’t really know what year this is from — my guess is late 1940’s. Perhaps someone that can remember when a ham sandwich was 25 cents can lend their expertise. Here are some closer looks:
I’m guessing that a “plain” milkshake vs. a milkshake with “ice cream” was a glass of guernsey milk shaken up. Remember, back then it was “real” whole milk so that would probably give you a nice thick frothy plain milk shake.