For LH, they can take a page out of XSeed or Aksys:
One or two OSTs
Cloth map of the Yamato islands, either full color or monochrome
The Log Horizon crest, either a decal or badge
Booklet done game manual wise is a good idea, or one done in a tabletop rpg style: ala D&D or Pathfinder with character creation, dice mechanics, etc.
* Sings* Please won't you push me for the last time, Let's scream until there's nothing left So sick of playing, I don't want this anymore. The thought of you is no fucking fun. You want a martyr, I'll be one because enough's enough, We're done. Vic: You told me think about it, well I did. Now I don't wanna feel a thing anymore. I'm tired of begging for the things that I want, I'm over sleeping