There are urban buses that connect the town of Mesolongi with the suburbs and few beach places in the region. There are also suburban buses to transfer to villages at longer distance and various towns around Greece.
As Mesolongi is centrally located in western Greece, a nice option would be to rent a car and make a road trip to the region. There are no car rentals in Mesolongi. The closest rental agencies are located in Patra, less than an hour by bus from Mesolongi.