You unlock the other islands by completing missions. The Green Sabre unlocks the second island, and Yay Ka Boom Boom unlocks the third. As for flying, you really have to figure out the majority of that on your own.

San Andreas re-introduces the notion of expanding your control over businesses and operations around the state - you will also have the ability to construct and operate your own Casino with some Triad friends. "You will also have the ability to construct and operate your own Casino." Having your own gang - it was first introduced in Vice City

Many of the optional cheats from the original GTA: San Andreas return in the Definitive Edition. There are some, such as some of the codes that change all pedestrians, as well as certain weather Combat Shotgun: GTA SA Appearances. Combat Shotgun Spawn Locations in GTA San Andreas Where to find the Combat Shotgun in GTA San Andreas: Found at The Four Dragons Casino in Las Venturas (After collecting all 50 horseshoes). Found at the LVA Freight Depot in Las Venturas, in the northwestern part of the district, hidden in some bushes. For Grand Theft Auto: San Andreas on the PlayStation 2, a GameFAQs message board topic titled "Any cheats to unlock everything before you do the first mission *Read*".
Tutorial for how to unlock all the properties in Grand Theft Auto San Andreas!This will work if you don't skip the story video on the begining and type the cheat "ROCKETMAN" when the
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gta san andreas unlock all properties cheat