Highly doubt that even a friendly crew would be willing to take food that you bring on board and then serve it to you. Not only would it disrupt their normal service flow, but I'm sure the other pax would inquire when they see a nice tub of caviar going out to you (and only you), not to mention liability issues, etc.

If you want to bring your own caviar and fixings and eat it yourself, without the crews involvement, then of course that shouldn't be an issue. No different than if you picked up Burger King before boarding and brought it on.

And while I think it's legal (?) for a flight crew to serve alcohol brought on board by a pax I'd say it's doubtful they'd be ok with opening a sealed duty free bag.