When the crew enter Maggie's Tearoom, Parker orders a cup of tea from the hostess, which actually is hard liquor poured by the bartender. Next to that bottle of liquor is a bottle labelled "J.J. Sefton Bourbon Whiskey." The name is a sly nod to the black-marketeering, conniving POW sergeant (portrayed by William Holden, who won an Oscar for his performance) in 1953's Stalag 17.
Even though the title is 'The Return of Maggie' there has not been a Maggie in the run of the series. But there was in 'Orange Blossom for McHale' (season two), a Kate O'Hara that is very similar in all ways to Maggie.