Rabbits and guinea pigs do best with a variety of leafy greens such as dandelion leaves, radish tops, carrot greens, collard greens, mustard greens, kale, wheat grass, dark lettuces (NOT iceberg), and some herbs such as basil, parsley, or mint. These are greens that I used to feed my rabbits but I do know you are not supposed to overdo it on spinach and kale (once a week is fine) because they have compounds in them that can cause issues with calcium levels. Greens are much more important than actual veggies because of the nutrients they contain, but some veggies such as zucchini or carrot can be given on occasion.
Ash, morning glory leaves and oak leaves are toxic to rabbits and most animals in large quantities.