You will need some Dirhams…get them at the airport (cash machine), make sure you change them back there too. Once you’re through customs there is nowhere to do it!
As mentioned above, a trip to the hammam is worthwhile. Get covered in the savon noir (black soap) and you’ll have never been as clean in your life. An hour long, full body massage would be good and fairly cheap too.
Do get out of Marrakech, I found it too claustrophobic and was ready to leave after the first day…I’d spent the previous 5 days crossing the mountains which were amazing!