Reddit reviews The Lesser Key of Solomon

First of all, that's amazing. Great idea for a dice box or dice rolling tray.

Have you considered something like a holder for minis, dice, pens/pencils? Basically little compartments inside for a player kit. I've seen a websites selling custom wooden enclosures for dice, pens, and minis for D&D players but a copy of the Necronomicon for a CoC game would be amazing.

Book ideas:

• There are a lot of collections of HP Lovecraft tales, many of which have great covers. I would particularly look for ones that have especially popular titles on their covers. "Call of Cthulhu and other tales" looks more fun than "Tales of HP Lovecraft." Of course, cool looking covers trumps all. https://www.amazon.com/Complete-Cthulhu-Leatherbound-Classics-Collection/dp/1435162552/
  
• King in Yellow (as SamEire93 said)
  
• Necronomicon (as you said)
  
• Der Hexenhammer - an actual book often referenced in CoC and with a really cool name.
  
• Malleus maleficarum - A translation of the Der Hexenhammer which still has a cool name.
  
• The Lesser Key of Solomon - A real book sometimes used in CoC games and which has a cool cover. https://smile.amazon.com/Lesser-Key-Solomon-Aleister-Crowley/dp/0998136417
  
• Book of the Dead (Egyptian version) - An actual book often referenced in CoC and with a really cool name.
  
• The Book of Eibon - I'm not sure there are any decent looking copies that exist, but the concept is good.
  
• Penny Dreadfuls: Sensational Tales of Terror - has a cool looking cover: https://www.amazon.com/Penny-Dreadfuls-Sensational-Leatherbound-Collection/dp/1435162765/
  
• Lovecraft Country - Maybe? It's a great book so I'd feel a little weird having it hollowed out, but a fan might really like the idea.