You will want this to be fairly all inclusive depending upon where you are headed and the likelihood of bike shops on the way. For instance, in our current ride through the Baja peninsula, we are finding bike shops once every 100 miles or so.
Lets get started shall we… If you are going any great distance, like across your state, you may consider taking a spare tire. At least 2 tubes, some spokes, lube – best we found so far is a wax based lubricant which helps to shed dirt and grime. A flat repair kit with extra tubes of glue. If you are given a kit as a gift from a friend who hasn’t used it in a while, make sure the glue is good and then get an extra tube anyway. I used a kit that I had for a very long time and found the tube was empty when I went to use it! Allen wrenches, spoke tool for repairing popped spokes, phillips and flat head screwdriver, wrenches to fit bolts on bike, many times you can get an all in one tool that will encompass all these tools, spare brake pads, spare cable[s], good duct tape or electricians tape [a trick is to wrap the tape around a pencil and then use some heavy duty cutters to snip off the ends of the pencil, this way your tape will be compact and not space consuming, super glue – duh, its super glue, some zip ties and whatever else helps you feel comfortable and ready to tackle repairs in the field. One great tool that is rarely mentioned and can be purchased from a couple companies is the rear gear removal tool. I am pretty sure this can be purchased for around 20 dollars from the Adventure Cycling Association, with out it or some other tool, you will not be able to replace broken rear wheel spokes.
Spare spokes, this is something you really want to have looked over by a person who knows bikes, again, the Co-op is a great place for knowledge. Also, you will learn on the road and amaze yourself at your own inherent ingenuity. Don’t be scared, ever!