I usually grab a packet of the Numi Green Tea (or Jasmine Green) to drink on the plane (ask the FA for cup of hot water).

I'll sometimes grab a pack of cookies or crackers or carrots or a banana to eat on the flight (if its a long TPAC, TATL, or transcon).

Ithink that grabbing a few items (ie 2 or 3) is okay. However, over a dozen cans of juice (or a dozen tea bags) is utterly inappropriate behavior, IMHO.