Sweet onions are at the top of the list. I don't think I could cook without having onions.
Green beans, corn, salad fixings, asparagus, brussel sprouts, and potatoes which I think should be a food group by themselves but which I now limit because they are so high in carbs.
The challenge hasn't been eating lots of veggies, the challenge has been learning how to cook them in ways that don't add useless calories.