It says it's done by rank - Here we go. And yes, I'm being really picky, though I don't think 2-1 vs. 2-2 makes a difference.

Rank 10-1 (Vanguard) (6 Boxes)
Each box had:
Power Star (x1)
Shadow Star (x1)
Divine Star (x1)
Spark of Life (x2)
Three boxes also had:
Radiant Fire Crystal (x10)

Rank 3-1 (Squire) (3 Boxes)
Each box had:
Divine Dust (x1)
Shadow Dust (x1)
Power Dust (x1)
Spark of Life (x1)
One box also had:
Warm Fire Crystal (x10)

Rank 2-2 (Apprentice) (15 Boxes)
Each box had:
Spark of Life (x1)
Divine Mote (x1)
Power Mote (x1)
Shadow Mote (x1)
Four boxes also had:
Dim Fire Crystal (x10)

Rank 2-1 (Apprentice) (25 Boxes)
Each box had:
Spark of Life (x1)
Divine Mote (x1)
Power Mote (x1)
Shadow Mote (x1)
Thirteen boxes also had:
Dim Fire Crystal (x10)

Rank 1-2 (Recruit) (4 Boxes)
Each box had:
Shadow Mote (x1)
Divine Mote (x1)
Power Mote (x1)
Spark of Life (x1)
Three boxes also had:
Dim Fire Crystal (x10)

Rank 1-1 (Recruit) (10 Boxes)
Each box had:
Shadow Mote (x1)
Divine Mote (x1)
Power Mote (x1)
Spark of Life (x1)
Five boxes also had:
Dim Fire Crystal (x10)

(Yes, I know I have too many knights)

Summary:
All seem to get one of each type of Sprite Food Item appropriate to their level, and a single spark of life, except vanguard gets two (could be off on that, but have no middle points to test). Also seems like ~50% chance of getting 10 appropriately-leveled Fire Crystals.

Close enough? Fill in the gaps?