while "grip" sometimes denotates a specific amount of money ($10G), it is also an expression with pimps, hustlers and gangsters for any large amount of money one is holding on to ('grip') and not letting go of except in an emergency (posting bail, paying damages, getting out of town, etc). This is known in the square world as "prudent reserve" (3 to 6 months living expenses).
youngsta: "I want to get some sick-ass'd rims for my ride!"
OG: "You betta hold on to your cheddah! You gots to stack your grip, young brotha!"