What do we owe those of our fellow citizens who are worse off through no fault of their own?

nothing

Explanation:

Its true that we don't owe them nothing however if we want to make this world a better place where people live in peace and alongside each other then giving a few pounds to charity or volunteering and helping out the needy can really make a change.

the economic activity signified in that scenario is a. production

in general, market production makes reference to the elaboration of a product or service which is destinated for economic purposes (to be sold) at money-price in a market. such product or service has to be principally tradable for money.

there is no money exchange involved in distribution, generalized reciprocity or balanced reciprocity.