I do this:
– line bag with cut-down bike box from Halfords to give it extra stiffness.
– let a little air out of shock, forks & tyres.
– take disc rotors off wheels & wrap in bubble wrap.
– remove QR skewers, wrap and tape to frame or put in bike bag pocket
– remove rear mech, wrap & tape inside rear triangle.
– leave chain on in big ring.
– remove pedals, wrap & tape to frame.
– remove handlebars and tape to wrapped fork leg.
– put pad spacers into brake calipers.
– Frame spacer into rear drop-outs & fork spacer into fork dropouts
– large foam cut-out under BB/outer chainring to protect & tape one crank to chainstay to keep in place.
– liberally apply bubble wrap/foam/plumbers lagging to frame.
– apply some more bubble wrap/foam/plumbers lagging.
Stick it all in bag, along with as many tools as you think you can get away with, knee/elbow pads wrapped round frame, energy drink powder etc…