Do something that you think you will be comfortable selling eg. clothing, pet food, computers, computer parts & accessories (flash drives), just about anything that you know consumers will want to have and will beat a track to the retailers’ store to get it.
I had to do a similar presentation in a group and we came up with this fabric softener that leaves your clothes wrinkle free hence no ironing. We put together an excellent presentation and in the end everyone was sold including the lecturer.
The key to your presentation is not what you sell but how you sell it. I would encourage you to use MS Powerpoint presentations for your class. Make it interesting and believable. Offer volume discounts, warranties, and guarantees within reason. The aim of the presentation is to show your teacher that you understand the concepts taught and you can demonstrate a practical approach to the concept so choose your product, call a few retailers of the product to determine what they are getting in terms of warranties and guarantees etc and use the info as a selling point in the design of your presentation. Remember to sell your product based on FAB (features, attributes and benefits of the product) using the steps in selling. Focus more on the benefits. Introduce yourself and your "company" (invent a name) and say what you are selling. Pretend that someone in the class was the retailer and ask him/her for the order at the end of your presentation. Please see the following link. All the best!

http://retail.about.com/od/startingaretailbusiness/a/product_select.htm