How many joints can you crack and how? Pretty straight forward.
Here's my list, from top to bottom:
- Jaw; by opening and pushing on joint at the same time
 - Neck; either by tilting my head either side, or by turning my head to full turn and pushing with my hand
 - Middle of my back; by pulling my shoulders back, or by lifting my arms and pulling them down whilst pulling my shoulders back (like the movement you'd do on the lat machine at the gym)
 - Elbows; by extending my arms quickly from bent to full lock out
 - Wrists; by pulling and twisting my hand whilst flexing the wrist
 - Hand (fleshy bit where the thumb meets the hand); by pressing on the fleshy bit of the hand next to the thumb and bending the thumb back
 - Fingers/Knuckles; everyone's favourite - by pressing the fingers down onto the hand at the knuckles, or by twisting the fingers individually at the joints
 - Lower back; by twisting my trunk at the waist
 - Ankles; by fully extending my foot and pushing it further either with my hand or the other foot
 - Toes; either by flexing the toes hard, or by pulling them individually at the joints