Candy!

• Chocolate Frogs - a treat on the Hogwarts Express cart which come with Famous Wizards Cards.
• Acid Pops - candy bought at Honeydukes in Hogsmeade that burns holes in your tongue
• blood-flavoured lollipops - treats for vampires
• Butterbeer - frothy, buttery hot drink served in The Three Broomsticks, a pub in Hogsmeade
• Cauldron Cakes - a treat on the Hogwarts Express cart
• Chocoballs - a chocolate sweet sold in Honeydukes
• Cockroach Clusters - a gross sweet made of cockroaches sold in Honeydukes
• Drooble's Best Blowing Gum - a treat on the Hogwarts Express cart
• Every Flavour Beans - Jellybeans that taste like every flavour imaginable.
• Fizzing Whizbees - levitating sherbert balls
• Ice Mice - gum bought at Honeydukes in Hogsmeade that "make your teeth squeak and chatter"
• Jelly Slugs - a sweet sold in Honeydukes
• Licorice Wands - a treat on the Hogwarts Express cart
• Pepper Imps - candy that makes you breath fire
• Sherbert balls - candy bought at Honeydukes in Hogsmeade that let you levitate a couple inches from the ground while sucking on them
• Sugar quills - delicate sugar spun quills that you can suck on in class "and just look like you're thinking what to write next." (Ron, Book 3)  Sold in Honeydukes.
• Toothflossing Stringmints - not much is known about these
• Whizzing Worms - not much is known about these, either

Where to buy all of these? Honeydukes, of course! It's a shop in Hogsmeade.