Skate ranch pieces challenges
After task Buy the Dino Head you can complete missions from Mindy on the skate ranch (violet star on compass). You have to do one trick on every new obstacle. For completing all tasks you unlock a few specials skaters.
You can find a drunkard in every district (dollar icon). He will want to see a few tricks (for example manual for 6 seconds, kickflip 3 times in one minute etc.) for money. You can do that task as many times as you want because these guys don't disappear.
You can help tagging graphitic guy (spray icon). He always gives you 20$ for one work. Find white cloud on the wall, there you must paint.
Get on Bmx and find Rick Thorn (bike icon). For doing tricks (like in drunkard challenges) he will pay you cash.