Which part of Sicily are you going to? I used to live in Palermo
There's a lot of really cool things to see all over the island. In Palermo- Montreale, Mondello beach (my favorite), Saint Elia beach (this is smaller and a little harder to get to), Cappuccini crypt, Palazzo Normanni, the cathedral, and good shopping in the center of the city. There's also usually some kind of fairs going on around the beaches, they have little rides and market stalls etc. For the rest of Sicily, there's great ruins at Agrigento in the south, I really liked doing those but it is HOT there lol and there's almost no shade. In the East there's Mt Etna and Taormina, Taormina is gorgeous and has a lot of fun little shops and bakeries. Hope that gives you some ideas!