The concept, unlike many in medieval Christian iconography, comes straight from the Gospels. "For I was hungred, and ye gave me meat: I was thirsty, and ye gave me drink: I was a stranger, and ye took me in: Naked, and ye clothed me: I was sick, and ye visited me: I was in prison, and ye came unto me." (Matthew 26:35-36, from the one and only King James version). This is the road to salvation, so it is perhaps unsurprising that a wealthy patron might wish to have himself commemorated performing these acts, as appears to be the case in All Saints, North Street, where a benign, bearded elderly gent presides over every panel.
The acts of mercy are represented in the two central rows of panels. The bottom row contains images of kneeling donors and an image of the sun and planets, which may or may not actually belong here.
To feed the hungry, the virtuous man doles out loaves of bread to beggars with the help of a faithful servant.
To give drink to the thirsty, he pours liquid from jugs into bowls with the aid of the same wee servant. Note that the figure in front is walking on padded knees with little stools under his hands; one of the desperately needy.
He takes in the stranger by welcoming a couple of travellers with walking staffs into his home. I'm not too sure whether that is supposed to represent a cockle shell on his hat, indicating that he too has been a pilgrim to Santiago de Compostella. I may be over-reading it here.
He clothes the naked with some spiffy red garments, once again with the help of the faithful servant. Medieval guys wore boxer shorts evidently.
He visits a sick man, bringing some sort of gift - might be money, or bread, or home baked goodies. Probably money, I think. The wife of the sick man seems quite overcome. Note the commode by the bed. The 15th century glaziers of York were quite partial to this as a symbol of illness or impending death.