The four 'noble usage's', are: contentedness (of the monk) with any robe, contentedness with any alms-food, contentedness with any dwelling, and delight in meditation and detachment. In the Ariya-vamsa Sutta, (A. IV , 28) and similarly in D. 33, it is said :
"Now the monk is contented with any robe, with any alms-food, with any dwelling, finds pleasure and enjoyment in mental training and detachment . But neither is he haughty on that account, nor does he look down upon others. Now, of a monk who herein is fit and indefatigable, who remains clearly conscious and mindful, of such a monk it is said that he is firmly established in the ancient, noble usage's known as the most lofty ones."
Full tr. of Ariya-vamsa Sutta in WHEEL 83/84.