The part of Miss Lyons, the secretary that Danny and Bernie's boss is "plugging", is played by Rosanna DeSoto who went on to appear with Lou Diamond Phillips in both "Stand and Deliver" (1987) and "La Bamba" (also 1987).
Ada Maris, (who played 'Caaaaaar-men' (from Shipping) the fine looking woman that works with Dan and Bernie, played the mom on the Nickalodeon show "Brothers Garcia" and has made cameo appearances in "Ressurection Boulevard." on showtime.
The actress that plays Crystal (the blond at the bar that makes the squeaking bottle sound when Bernie rubs her head) is Rebecca Arthur who played Bronson Pinchot's girlfriend on the classic 80's series "Perfect Strangers.
Actress Sachi Parker, who plays Carrie (Debbie's friend who, during the softball at the beginning of the movie, is being told that she should ask her live-in boyfriend to pay half the rent) is the daughter of actress Shirley MacLaine ("Terms of Endearment").
If you are a big MustSeeTV person, you will notice that Demi's (Debbie's) best friend in the movie, outside of Elizabeth Perkins is Megan Mullally. She plays 'Pat' ("nine-oh, nine-oh") and is at all the luncheons and the out door baseball scenes w/ Demi and is at the New Year's Eve party dancing and getting up on Rob Lowe. She plays Karen on Will and Grace.
In the scene during Debbie's company Christmas party, the waiter is serving drinks and there are three people standing around, one of them is actually Willie Gault who was a star receiver for the World Champion 1986 Chicago Bears.
Indie film queen Catherine Keener makes a small appearance as a waitress in the bar, telling Bernie (James Belushi) to chug his drink while Dan (Rob Lowe) & Debbie (Demi Moore) are having their New Year's quarrel.
Concerning the lack of McDonalds at Broadway and Belmont, there in fact was a McDonald's on Broadway near Belmont. I lived in Chicago in the early 80's and got off the El at Belmont and then walked up to my apartment on Broadway. I ate many times at that McDonalds.
In the scene where Debbie & Joan go on a double date, Colin (Tim Kazurinsky) who is sitting next to Debbie, actually wrote the screenplay for the film. You may also recognise him from the Police Academy films as he played Cadet Sweetchuck!