That's what I've said twice now, I want to know why puchasing things will give him pleasure. Let me explain my viewpoint...
I don't think that the original depression is directly related to having enough material posessions. I think something else would be the cause, so I'd like to know what buying things offers to temporarily dispel the depression.
I do not believe that one form of happiness can dispel a deeper, unrelated unhappiness - therefore I think that there is an association in purchasing that may temporarily address the deeper problem in some way, although whatever the association is it can merely be peripheral because long-term (and perhaps medium-term) ownership of the item doesn't seem to help.
I expect it is something to do with the idea of acruing items, although whether this is merged with a sense of productivity or social standing - I cant tell.
It would also be interesting to know whether there is a pattern to what the OP would purchase