Well that is an extremely interesting effect; "Wyvern: grants food effect".
Guess DD type food would increase the wyverns DoT as they don't weaponskill per say and dmg/str/att doesn't affect elemental breaths.
On a different note, should one use defense food, this would increase the wyverns survivability.
What seems most potent to me though, perhaps others may disagree, is eating HP+ food and as such granting wyverns a higher HP leading to a higher floor healing breath return. If one should use carbonara which i believe increases HP and sTP then ones wyvern would also gain Tp quicker also leading to higher healing breaths.
Obviously the DD stats are superb, weaponskill piece and tp piece, shouldn't really need to be said.