This can be difficult; it all depends on the person. If someone is very ill, buying ahead of time and tucking gifts away for future can be comforting to them and helpful to the person left behind who will have to take on that role of buying gifts. A person may choose to make a list of things they might buy rather than actually buying them ahead of time, as a guideline. So it really depends on the person and what is important to them. Perhaps your father can think of past gifts your mother purchased and use that as a guide.