I find all the above interesting and all possible as songs seem to change over the years. I simply thought if was about people eating the same food every week. Like a schedule. I had some friends that had same dinners certain days of the week. There was even a Prince spaghetti commercial about "It's Prince spaghetti day!" Also in some religions, Friday was a non-meat day-thus a fish day. When my kids were little we often did pizza on Fridays since it required no cooking and the chance for me to relax on the last "work" day of the week. Of, course we know moms work everyday regardless. Have a great week!