Tools, pump, tubes, patches, good glue, appropriate spare parts, clothes for weather changes, first aid, food, water, and, if you're really getting far out on the fringe, some sort of minimal bivvy equipment. And something to carry all this in. Plus you want to leave word behind with someone about your route and estimated time of return. For tools, the standard tool kit for any mountain bike ride will suffice. This is a pretty basic kit.
Some folks carry more, some less.
The further from civilization you plan to venture, the more inclusive your kit ought to be. Maybe you'll be lucky enough to have someone come along who can work on a bike and thus will be able to save your ass where you couldn't. But if you don't know how to work on a bike, learn. Make sure your pump works on your tubes. And make sure that their valves will work in your rims.