I think taking food aboard is fine in principle, no matter what class you're sitting in, though I agree that smelly foods are at least as bad (if not worse) than loud music/conversations.
With the exception of the excellent UL cashew nuts, I'm rarely enthralled by the various salty snacks offered with the first drink rounds so will often take a pack of the following on board with me:
They go particularly well with champagne, and quite often are a better base for eating the cheese course later on. I have also been known to bring on some high cocoa % chocolate...
However I am but a rank amateur in comparision with the lovely guys I met on the PHX DO trip who come fully stocked with tonic, ice and lemon slices for a succession of G&Ts