Complete the indicated task in the listed mini-game to unlock the corresponding item for use outside of that game in Free Play mode.

Halo Covenant Ghost: Win a silver medal while driving the Covenant Ghost in the Imperial Raceway mini-game in Cherry Blossom Grove.
Halo Grunt Doll: Win a gold medal in the Lakeland Dash contest at Suri Mountain.
Halo Warthog Racer: Win a silver medal while driving the Warthog in the kart racing mini-game in the temple area.