Most birds can actually eat just about anything humans can. There some things that they should only have a limited amount of and very few things which they absolutely cannot have.
Things they cant have:
Avocado
Chocolate
Coffee
Iceberg Lettuce
Apricot
Asparagus
Peach - the seeds
Hemp
Garlic - Ok in small amounts
Those are the common ones. If you google toxic foods for birds you can probably find a complete list.
Also most seeds or pits in fruits/veggies are toxic so make sure to not give them as a whole. And then there are others such as strawberries which are commonly sprayed with pesticides so generally isn't recommended but personally i have a given strawberries to my birds before and they LOOVE them but boy are they are messy. It is recommended that you should feed only organic foods but it's not mandatory, if you wash them well before hand it should be ok.
Also nuts are great protein too. My senegal parrot adores almonds and peanuts(unsalted) just make sure to not give too much but a couple here and there is great protein for their diet.
You even give egg, or chicken(i don't know why but i find this weird to give birds chicken and egg... it's like cannibalism almost ...lol) I've never actually given my birds egg or chicken aside from some egg food sprinkled on top of their pellets a once in awhile. So you would have to look into the specific ways that are ok or i can look it up for you in a minute.
Mashes are quite common in the bird world. A lot of people give their birds a mash which can include a variety of veggies and fruits and nuts even mixed together and often people make a huge batch and freeze it and then warm it in the morning and then they leave pellets or their regular food in the cage through out the day as a snack.
That also reminds me to mention that if you do give fresh foods make sure to remove it after an hour or so it doesn't get all bacteria filled and so on and harm and make your bird sick.
Brown rice is also ok to give and another thing people often put in mashes. Grains and plain pasta(even uncooked pasta) is enjoyed by many birds.
Also more ideas in the link below.
Feeding Large/Small Birds: Protein, Whole Grains, Nuts, Fruits, Vegetables
I'll ad to this tomorrow. Hope that helped for now.
