The Tunisian government has recently enacted a new fee that non-residents must pay in order to leave the country.  You could miss your flight and be barred from leaving if you fail to purchase the Solidarity Stamp [Le Timbre de Solidarite] before leaving.  The stamp is not sold by airlines and is available only in a limited number of stores, and it costs 30 dinars. 

Add this step to your departure schedule so that you don't miss your flight.