Char Aznable:
Play Simulation Program 1 and reach rank "S".


Garma Zabi:
Play Simulation Program 2 and reach rank "S".


Sayla:
Play the federation missions and reach at least rank "C" for three times.


More missions:
Complete the game.


Austin's Zaku 1 federation shield:
Complete the game, then play through practice mission 1 with Austin's Zaku 1 and complete it. You get a heavy federation shield like the Gundam's, and some new supplies.