A beloved parent or revered family head is coming for their first visit, and due to years of lies told through letters to them, the leads have to pretend to be married/unmarried/have children/practice some other profession, etc.
Which reached an absurd apotheosis with Richard Haydn, a terrific actor in any event, playing a Japanese client of McMann and Tate named Mr. Mishimoto on Bewitched. (He had a love of the "oriental" gourmet dish Hong I Wong Goo Rosh.)
Lassie even had amnesia in a 4 episode arc that lasted all of January 1970. Seriously upset me as a child, as I thought she'd never find her way back home.
Something important and/or sentimental gets accidentally thrown away/donated and everybody has to scramble to get it back.
The leads have to substitute for a friend in a pinch doing something they're totally unqualified for: running a restaurant/ice cream parlor/gas station/shoe store, etc...