Quite a lot of the stuff that I put on my hair I would be able to consume, my Dad laughs when I put Cayenne pepper or mayonnaise in my hair. Here is a list of things that are edible but also benefit your hair!
Apple Cider Vinegar - Removes buildup, leaves hair shiny & smooth, makes hair easier to manage and is said to promote hair growth. For an ACV rinse mix 2 cups of water with 1/4 ACV.
Egg - Our hair is made up mainly or protein and so are eggs, therefor the egg strengthens hair. You can also get the same effect from putting mayonnaise in your hair.
Cayenne Pepper -Stimulates circulation in the scalp which results in faster hair growth. Mix the pepper with an oil, be careful though because it can become very hot!
Onions - Are used as an 'old herbal folk medicine' for baldness. Grate an onion and massage the juice and onion into your scalp.
Glycerin - Is used for sore throats and is also well known for its moisturising properties, so is brilliant for dry hair! Mix roughly 30% Glycerin with 70% water and apply to hair.
Oils - Oils such as Olive Oil, Coconut Oil, Avocado Oil and Grapeseed Oil are all great for your hair. Use them before you shower and wrap your head with a hot towel to encourage the oils to penetrate the hair and scalp. You can also use them after a shower to seal moisture into the hair.
Well that's all i can think of at the moment but if you have any more edible things that benefit hair then feel free to leave a comment :D