I agree that you should be sure to have an advance directive on file with your doctors, hospitals, and family, so there is no question about your wishes. You can plan for a surgery down the road, but not your everyday type trauma emergency.
Iron infusions, erythropoitin, and other preoperative strategies to increase your circulating blood are good (if you have time, since it takes about a month to make enough blood). But, it does not deal with the instance of sudden hemorrhage, which is often fatal without proper treatment.
Even if you cannot accept even autologous transfusion, you might be able to accept the notion of cell-saver technology, that returns the blood to you as you bleed. Please look into it as an option (if available in your area).
Here is a link to an article that discusses the issues and possible solutions:http://ceaccp.oxfordjournals.org/content/4/2/35.full
Good luck, and good for you for trying to do advance planning!