Championship Boxing is a moderately-rare Sierra release. It is packaged in a box similar to Stunt Flyer and Wrath of Denethenor. In good condition, it fetches a healty price around the community. Depending on several factors (and who is wanting to buy the game) I have seen it sell from around $30 to over $100 for a sealed copy. It sounds like you have a complete release by your description, what condition is the box and materials in?Also what platform is it for?
I have two copies of this game. One sealed release in mint condition for Com 64/128, and an open version for IBM, with everything you list minus the warranty card. The opened versions box is a little ragged at the opening, but otherwise fine. Unless the warranty card is something radically different from the ones that Sierra normally included, we should be fine on having meterial here at my place to scan for the continuing archive project. Would you mind posting a scan or picture of the warranty card? Thanks!
Let me know if you have any more related questions about CB, or any other older game.