"Giving money to UNICEF/OXFAM/Compassion is regarded as an act of charity in our society. The bodies which collect money are known as "charities." These organizations see themselves in this way - if you send them a check, you will be thanked for your "generosity." Because giving money is regarded as an act of charity, it is not thought that there is anything wrong with not giving.
The charitable man may be praised, but the man who is not charitable is not condemned. People do not feel in any way ashamed or guilty about spending money on new clothes or a new car instead of giving it to famine relief. (Indeed, the alternative does not occur to them.) This way of looking at the matter cannot be justified. When we buy new clothes not to keep ourselves warm but to look "well-dressed" we are not providing for any important need. We would not be sacrificing anything significant if we were to continue to wear our old clothes, and give the money to famine relief. By doing so, we would be preventing another person from starving.
It follows from what I have said earlier that we ought to give money away, rather than spend it on clothes which we do not need to keep us warm. To do so is not charitable, or generous. Nor is it the kind of act which philosophers and theologians have called "supererogatory" - an act which it would be good to do, but not wrong not to do."