I go to the one here every year. There are 12 shops this year all over our 'valley'. At each of the shops they have something that they are doing a demo on. That is their 'special' item just at their shop. They also have a quilt that they have all done, sometimes it is a mystery, sometimes it is hanging for all to see. Each shop does different colors on the quilt. You get one 'piece' of the quilt at each shop. If you don't visit a shop you won't get that 'piece' of the quilt. Sharing is discouraged because of copyright, the shops usually buy the pattern for the shop hop.
It is not necessary to buy and any of the shops. The only thing for us is that we have to purchase a 'passport'. Ours is $5.00. It is a card that has all of the shops listed with the rules on the back. We also receive a 'charm' when we purchase the 'passport'. At each store you watch the demo and then they will stamp your passport. Each store has a special stamp. You have a specific amount of time to make it to all stores. When you visit the last store on the hop you leave your 'passport' at that store and they throw it in a pot with all of the other 'passports' for the drawing of their grand prize. Ours is usually a sewing machine. They also have other prizes too, but can't remember what they are.
They are a lot of fun and even better when you take a pal with you. You get to see some neat tools of the trade and of course you find stores that have just the right fabric you have been looking for.
I hope this helps!