How do a god or a demon high on his spiritual rank benefit from interacting and doing my will?
Anymore recurring to Yahveh help and power seems coherent with my philosophy, Spirits have their own agendas and interests and Judeo-Christian objectives are opposite ti mines.
What can an offering such as water and a bit of food offer to that big guys really?
It’s really to show devotion rather than actually obtaining energy from the food.
That and they can taste the food just like me and you.
If you were on a forum and someone asked about something, where you had the knowledge to easily help them, you’d probably do it, because it feels good to do things you’re good at and enjoy.
Power seeks expression, life seeks more life, consciousness seeks objects to think about and problems to solve. 
Demons are kind of like astral Trekkies, they have this BIG enthusiasm and won’t let anything get in their way, and (at least some) angels are like athletes “in the zone,” totally blissed out in the purity of form and function becoming one thing.
(Insert sex joke here)
In all seriousness, they want to help. Just like we want to help. Its a win win situation. Especially since their energy gets to have platform on this plane.
They don’t call it the Big Bang for nothing! 
Artfully stated.