The MacGuffin for my character design idea is going to be some form of space fuel. Energy or fuel for the characters' space ships. This space fuel is only found in certain places.
The bikers goal is to get this fuel/energy from guarded space stations and planetary complexes. The fuel is being produced by a military force or government. This space fuel is expensive and only sold to those who can afford it. (Or they hoard it all for themselves) The bikers steal this fuel and give it to the poor colonies on planets scattered across the galaxy.