Stick Up ArtistG 30

The first island is good for grinding this achievement, should you need to after completing the story. It may also help towards the Crime Doesn't Pay achievement, IF you find valuables.

Method:

Drive to the area where the Endtimes outdoor supplies shop is. Rob it. Now run east to the Beanz coffee shop. Rob it. Finally run south west to the bar. Rob it. Run north back to Endtimes, which should now be open for business again.

Rinse and repeat!

As an aside, you don't have to actually take anything from the store. You just have to successfully kill / incapacitate the owner so the building blueprint shows up.