What needs to be on the outside of a board game box?

At a bare minimum you need to have:

The name of the game

The maximum and minimum number of players

The recommend age range of the players

Required for retail:

Barcode

Recommended:

A description of the game

The "average" play time

Box art

In addition to what you've stated it's good to have an idea of how long the game takes. Does it take 15 min? Does it take 6 hours? 1-2 hours? This is good to know before playing a game.

Also don't forget the box art, and some description of what the game is about. Without a description it's easy to forget if a game is about selling art or exploring a haunted house.

Oh, and the title should go there too.

And the name of the manufacturer.

And you can choose to put on the name of the designer. I am more likely to pick up a game if it says "Reiner Knizia's Through The Desert" rather than just "Through The Desert" because I like that designer.

You should include: playing time, degree of difficulty, and suggested age of the players. Good luck! (In the case of war games: solitare suitability.)