When Lisa and Stacy Lavelle are in the Simpson living room trying to settle on a name for their new doll, the boxes of dolls behind them already display the "Lisa Lionheart" name that they have yet to settle on (or even discuss).
Grampa Simpson gives the family a box of 1918 silver dollars. However, the US Mint did not produce silver dollars between 1905 and 1920, so these coins couldn't exist.