To Avoid:

• Annonacea (Graviola, Guyabana, Soursop, Stachelannone, Sauersack, Cherimoya, Custard Apple, pawpaw (don't confuse with the papaya which is also sometimes called pawpaw)...):
  Contains strong neurotoxins. Chronic use seems to cause neurodegenerative diseases similar to Alzheimer's and (atypical) Parkinson's. I would avoid it altogether. Comes as fruits, teas, softdrinks, anti-cancer supplements.
• Gingko teas:
  While Ginko is supposed to boost the brain perfomance, Ginkgo leaves contain large amounts of ginkgol acid, which is supposed to be cancerogenig and possibly neurotoxic. Gingko leaves are often added to teas supposed to support your alertness. I would avoid altogether. Medical Ginkgo products should be free of ginkgol acid and thus safe.

To be careful:

• Lemon myrtle, Estragon, Basilikum:
  Spices which might be toxic, cancerogenic. I would not be scared of the use as spices (extremely small amounts), but I would not consume large amounts or use for making tea.
• Stevia:
  There might be negative effects on male reproduction in high doses.
• Sweetener:
  Rat studies showed possible cancerogenity of some sweeteners in very high doses. Low doses should not be a big risk.

To consume:

• Tea (green, white, black...):
  Contains caffein and antioxidants. Both are supposedly healthy and caffein has the nice effect of also waking you up. However, check for other ingredients which might be on the list of bad things. Many teas are contaminated with pesticides - I would not be too scared, but I prefer teas with an organic food label, which should be free of pesticides. Addition of milk reduces the antioxidant properties, whereas a bit of citron enhances them.
• Coffee:
  Supposedly healthy similar to tea. I however prefer tea, since the coffein kick is less abrupt. Coffee wakes you up quickly and then lets you drop into a down after a short time.

Any suggestions which food to add or which food to conduct research on?

Later I will add references for my claims.

I'm looking forward to your comments.