One of the places Hal goes while trying to get the contents of his wallet back is the Circus Burger, where Reese worked briefly earlier in the series.
Caitlin Crosby, who plays Kelly, one of the popular kids in school also appeared in "Watching the Baby".There she was Joanne, one of the 3 girls who went to Malcolm's house to ask him, Reese, and Stevie to the prom because their boyfriends ditched them. Ironically, they're also involved in the prom.