How about a dozen…
Reasons to adventure (useful in making a PC's back story)
Histories of magic items (maybe a different DPF for weapons, armor, shields, etc.)
Special materials and their effects
Monetary systems
Household magic items (self-cleaning pots and the like)
Sets of magic bracers (the DMG is really light on them)
Paladins (all with slightly different moral codes)
Items every adventurer needs, and the uses thereof (uses for signal whistles and the like)
Out of battle curses (like 'Bob can never sleep in the same place twice' and such)
Points of view (one place described for PC's with; low light, darkvision, spot +10, etc.)
Exotic components (things to make scribing scrolls or making wands easier / better)
-Tatsu