Sugar and caffeine help increase concentration. Some people like this, some don't, it does "mute" the high of good haze (sativa), and get rid of couchlock from indica.
I know of no foods to preload on for smoking weed... Just hearsay that could be bullshit.
I remembered some hearsay that may be bullshit. This comes from me and my friends experience. I like to take a multi-vitamin. Then eat a balanced meal of meat, vegetables, and whole grains. Chase with a glass of water and wait 45 minutes. Your body needs energy and nutrients to avoid being "burned out."
EDIT: I have experienced and heard good things with chocolate. Also while not a food Tagement HB (sp?) supposedly helps.