Green food can be practically any fresh green leafy vegetable. When feeding grain, you also need to provide grit for the birds. Again mixtures can be purchased from the same stores you buy grain from. The birds get minerals from the grit. They also need the grit so that they can grind the grains in the gizzard to be easily digested.
Water is extremely important for pigeons.
They are heavy drinkers, especially in hot weather. Water should be fresh, cool and clean. You can buy fountains for your birds or you can make them. Water should be covered so bird droppings can not get into the water. Pigeons like to bathe.