I had very many favs in the past, carnivore changed it very drastically… But I still have a few favs I occasionally eat with my meat or eggs.
Onions and tomatoes. Both are quite sweet but it’s good, at least I automatically use a tiny amount
My current stew has both of them.
At the moment we have cucchini too (I lost interest but remember the times when I liked it).
Before carnivore I very often ate carrots and peas as well, in soups. I have nothing against carbier items on keto especially vegs as they are way more flavorful and a little goes a long way. All vegs are out if I want to eat them in big amounts anyway (if something is so super low carb that could be an exception, I dislike it or can’t get it here). I touched fried cauliflower, inevitable 40g net carbs in a few mins… I banned it right away, it was in the beginning of my keto times. But it still worked in soups as I used little…
But now (apart from my stews and eggs in purgatory) I just eat some spring onion or radish or pepper or cucumber with my meat sometimes. I like juicy and crunchy. In our household it’s a very important thing to have raw vegs to grab and eat. We never liked salads. I just don’t NEED it anymore. It’s just innocent fun 
Our typical pepper isn’t bell pepper but an almost tasteless, less bulky capsicum. I get juiciness and crunch and no noticeable sweetness.
Oh and I barely ever eat any but it’s nice, it’s among the very very few green leaves I am willing to eat: sorrel. It’s sour, so cool, I LOVE sour things. I like sour tomatoes and dislike very sweet ones too.
And it’s super easy to grow, one just toss some seeds into some soil and the sorrel patch will live forever. My soil is very bad, barely any vegetable grows there but my sorrels are thriving. They need exactly zero care, I don’t even water them.
I only eat a few leaves a year but that’s a joy.