There are a number of things that you could do for your Husband's 50th Party. 50th Party is special because it makes you feel that you are done with 50 beautiful years of your life.
In order to make it special for your husband, you would need to do some research and effort. You can invite all his friends from the past as a surprise and tell each of them to prepare a little speech for him.
Cook his favorite food for the party and tell everyone how he likes his food. You can also arrange a sideshow or video highlighting him and his moments with you.