Sigaloavada Sutta has alms offerred on behalf of the dead -- which is clearly a pre-Buddhist custom such as that mentioned in the first part of the Mahāparinibbana.
Tirokudda Kanda Sutta: has clean good and drink offereed to pretas, but the merit accrued is one's own.
Janussonin Sutta: http://online-dhamma.net/nanda/AccessTo ... .than.html
This sutras says that gifts made to one's ancestors who have been reborn as hell beings, animals, gods or human cannot be enjoyed by them. However, gifts made to hungary ghosts can be enjoyed by them. In all cases the donor enjoys the merit of the gift.
How does that apply to ganapujas and general offerings to various beings from the six lokas then? Enlightened beings don't even need our little offerings of course but Nagas, genii loci, gods etc. Does the "outer" offering then have any value at all?