Tangier in three days
Add a day trip to Chefchaouen, Tetouan or Asilah.
With three days you can see the city properly and still leave it once. Use the first two days for the medina, the Kasbah and the Cap Spartel coast.
On the third day choose one trip. Chefchaouen is the blue mountain town, Tetouan has a UNESCO-listed medina, and Asilah is a small whitewashed town on the Atlantic.
Chefchaouen is the longest day, Asilah the easiest. All three work well with a private driver.