Other than that it seems a clear out the refrigerator type of thing, nearly any protein you like or that you have, chorizo, a Spanish sausage, with chicken (dark meat), pork, rabbit, frogs legs, what have you. Onion, garlic, then vegetables, green beans, peas. Tomato sauce.
Saffron. Not particularly for color because tomato also colors the whole thing. So does paprika and your preferred chile powders.
Most versions finish with seafood placed on top after the rice is added and distributed. The rice will take 20-25 minutes. The pan is no longer stirred. The items are settled on top into the liquid.
The videos I've watched, the cooks do all sorts of bizarre things, like use chicken bullion, the lowest form of broth available combined with saffron the most expensive herb that there is. Raw shrimp added right after the rice too early, and finished with pre-cooked shrimp. For a Valencia festival four huge pans are prepared over open fires. These guys have done this for decades, they use frozen vegetables apparently and there is no seafood. Theirs is a simple version of chicken legs and vegetables. The whole point being the soccarat rice.
The mistake that restaurants make in the U.S. is to overload their paellas with everything possible all at once and that's why the Valencia festival version es muy auténtico and the restaurant versions try too hard and fail at achieving the main aim of socarrat rice.
Why do people have such a problem with rice?
There are different kinds of rice for different things that behave in different ways. It turns out that my all time favorite rice is the least popular, the least available, the most expensive. In the stores around here I see long grain rice, mostly for Spanish rice dishes, and Jasmine rice for its sweet floral quality, and plump short-grained Arborio rice for risotto. My all-time favorite is Japanese short-grained rice, somewhat starchy. I've used it successfully in risotto, sushi, rice balls, soup, and plain so it sticks and can be picked up with chopsticks. I wouldn't doubt it works with paella too.
This woman is a joke.
Kay has a cooking channel where she destroys everything. Her subscribers know she's not quite right in the head so in comments they treat her with great tenderness. Elsewhere they laugh. At her. She is the satire of food, popular for her enthusiasm and unawareness and her viewers, while kind to her are actually cruel for laughing behind her back. She is so wrong that she cannot even pronounce the word for the thing that she's trying to cook. You can skip, skip, skippity-skip and not miss anything.
Kay would do better by reading this page before starting. The video is one of those bless her heart things. All of her videos are this type of unintended satire based on sincerity. You can read through the comments on YouTube to see what is going on, and sort through her videos to see what not to do. What not to do ever. To see how a person can get things so wrong.
Here's a girl who does a fine job but makes a few strange choices.
Here's a Valencia festival presentation. No explanation, just lovely music. Their target is chicken flavored socarrat rice, the vegetables take a backseat and there is no seafood. Again, you can skip through it without missing anything
Here is an arrogant opinionated American chef. I don't see him using tomato sauce/paste, or white wine. He relays a few very good hints.