Officially around 6pm, unofficially more like 6:30–7pm depending on the day (island life: piano, piano), bars across town start serving aperitivo: a drink that comes with a spread of snacks included in the price, often generous enough to make a light dinner of it.
It overlaps with the passeggiata, the evening walk that fills Via Atenea around the same time, so the two are easy to combine: a drink in hand, a slow lap of the old town in between, or simply just watching from your seat as you sip a spritz.
A few places to get you started
A converted old bakery at the top of Via Garibaldi, in Piazza Giuseppe Sinatra. Widely considered the best cocktail bar in Agrigento, with the Michelin Bib Gourmand-awarded Osteria Expanificio next door for dinner.
A wide list of Sicilian wines by the glass, a complimentary snack board included with every drink, and a lively local crowd most evenings, opposite the Teatro Pirandello.
A focacceria with excellent sandwiches and good local meats and cheeses. It also runs its own Happy Hour, listed right on the menu, a drink with a snack board included.