For me:
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Broccoli
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Carrots
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Onions (even if they make me gassy as a mofo)
I love American Chinese food and most of the dishes feature these three veggies so I always have a banger of a meal when I order.
Honorable mention to green peppers too, a very versatile veg that goes well in anything.
I'd include nightshades but they're all tubers and fruits and I get angry about the culinary/botanical distinctions