The short answer
Plenty. The breakfast counters fry msemen and baghrir from about 06:00, Mechoui Alley sells pit-roasted lamb at midday, maakouda vendors on Rue Bani Marine fry spiced potato fritters, Chez Abdelfattah in Derb Dabachi sells mixed-meat sandwiches by weight, and Sfenj Boulabada makes the fried Moroccan doughnut. Each runs to its own time of day.
In more detail
Start early. The dawn counters near Bab Doukkala and in most neighbourhoods serve msemen and baghrir with honey, and soup counters in the lanes sell harira. Sfenj Boulabada in the medina specialises in sfenj, rings of fried dough, sold fresh and vegan by default.
Midday belongs to Mechoui Alley, off the northeast corner of the square, where whole lambs come out of clay pit ovens and are sold by weight with cumin and bread. Come before about 14:00, and not on a Friday, when many stalls rest.
For a quick sandwich, the vendors along Rue Bani Marine fry maakouda, crispy spiced potato fritters, usually served in bread with harissa. Chez Abdelfattah, a popular stall in Derb Dabachi, sells mixed-meat sandwiches of chicken, sausage and liver by weight. Near Dar El Bacha, the Sabich counter fills pitta with vegetarian and vegan-friendly toppings, and Mazel Café on Place des Ferblantiers serves falafel, hummus and wraps.
For fish, N°14 Krita on the square has fried squid, shrimp and sole since 1966, and a fried-fish eatery sits near the Ali Ben Youssef Mosque. The rule everywhere is the same: busy, hot and cooked in front of you.