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.
Broccoli, carrots, potatoes.
That may sound boring, but there are so many varied ways to season and flavor the above and they can go into so many dishes.