My wife does this. I sent her the link and asked her. She says if you have access to glow-in-the-dark yarn, make ghosts. It's a simple — I can't crochet to save my life and I'm not trying to learn, but you probably know how to do it. Spiral out to desired width and then maintain the rows (I'd call them rings though?) until you get to the bottom, then however you do the flanges (whatever they're called). It's probably skills you already have. Then sew on eyes and a mouth. Frowning faces sell better than happy ones for some reason.

She also suggests poison apples, but she had to buy that pattern. A lot of people call them pumpkins but they're called poison apples. They look like apples (or pumpkins, IDK) but they have a "slimy" cover, which is really just another layer of yarn, I think.

My wife doesn't do clothes or blankets — they take too long. She made some headbands. They never move. She's made hair clips. Those don't move either. People buy decorations they can put on their desk. Warm clothing is cheaper at thrift stores than you're probably willing to take.

Also — and this comes from me, not her — I once saw a crochet market stall where the price tags, if you flipped them over, told you how long they took to make. I think people look at crocheted gifts and think they're too expensive, they want it for the cost of the yarn or the cost of some mass-produced made-in-China plushie they found on Amazon. They don't understand the time cost. So if you know how long you spent on something and you price your stuff with respect to that, noting the time can help too, especially with so many people arguing for higher wages and whatnot. I'd go to a market and see what other crochet crafters are charging, and be real honest with yourself about what your craft is worth. If it's decent, even if you're starting out, you deserve to charge the same. Or maybe more. But some people are really good and charge accordingly, too.

Warm clothing, like scarves and beanies, will probably be in demand before winter...

I made a "garland" out of these little maple leaves (https://crochetstrends.com/...). They don't take long. Not sure if they would sell?

I don't usually buy things at the market because they're too expensive :(

So maybe try to have something cheap and cheerful also for sale? Like a sticker for $1 , or a little postcard?

You could do the shape shifting cupholder?
The snake/turtle curles up and screams when you put the mug on it.
Probably some scary video game pop colture things? Pacman ghosts - an empty heart container, a pink faery?

You could make keychains out of some tiny amigurumi.

It might not work for a halloween festival, but someone once suggested to see if there are any viral crochet trends on other social media sites that teens/kids are into.

I met a person on Facebook who was selling homemade hats. They were ugly as sin but this person clearly had the skill.

I commissioned them to make some rainbow toques which I sold as "gay ok" torques. I made a fucking fortune selling them.

I even told the guy like dude... Just make gay hats and take all the profit for yourself, you don't need me... He didn't want any part of it he just wanted to crochet.