The phrase "rid oneself of" means to eliminate or to get rid of something unwanted, unnecessary or harmful. Some antonyms of this phrase are to acquire, to accumulate, to obtain, to gain, or to possess. When we acquire or obtain something, we are adding to our collection of things instead of trying to eliminate them. Similarly, when we gain or possess something, we are trying to retain it in our possession. Therefore, the opposite of "rid oneself of" is to hold on to, gather and retain. Sometimes, we need to rid ourselves of certain things, but at other times, we may want to preserve them. Hence, it's important to understand the context before using the antonyms.