Although this film was explicitly set in 1987, while Carol is driving on the highway, she passes a burgundy 1992 Cadillac de Ville.
When Carol signs up to cook Sunday dinner at Wrenwood, she chooses the date April 6. In 1987, April 6 fell on a Monday.
Although the film is set in 1987, the rental car Greg and Rory depart Wrenwood in is a first generation Dodge Intrepid, which did not begin production until 1992.
At about the 25-minute mark, when Rory is reading his gang report to Carol and Greg (just after Carol sees the doctor), he says "...MAC-10s, killing numerous of innocent people." Neither he nor his parents notice that the "of" shouldn't be there.