Fruits man, bannanas, blue berries, strawberries, grapes. They are like gasoline for me. And if your lunch is too heavy, you might want to consider splitting it into 2 separate smaller meals. Over eating can zap you like that.
Look into ON's Amino Energy..2-4 scoops 30 mins before lunch should do the trick. I have to have my Amino's daily can't go without them. A little green tea and green coffee extracts are in there.