Onions, Carrots, Celery - I chose these vegetables (often called mirepoix) for the soup because they are common vegetables that you might chop up for a holiday meal. If you’re planning ahead, you can chop an extra portion while cooking for the holiday and they’ll be ready to go when you want to make the soup. If you don’t have those vegetables leftover, you just use onion or even use a combination of chopped onion and bell peppers.