Learners will need polymer clay to create the model. I specifically chose polymer clay (such as Sculpey or Fimo) because it will stay pliable for the duration of the class and then you can bake it into a durable model your student can enjoy for years.  If your student uses just one color (see below), you can buy a package for about $3 at a local craft store.  Alternatively, you can buy a big starter set with 30 or more colors for about $25 on Amazon.

I mostly used peach/tan (only one package needed).  I also used very small amounts of red/brown (liver) and extremely small amounts of  pink (tongue), white (teeth), green (gallbladder), and yellow (pancreas).  I will reassure students that they only need one color and I'm using the other colors to make it easier for them to see what I'm doing. You know your student best and whether you'll have mostly unused blocks of polymer clay when you're done or whether they will be put to good use for other craft projects.  If you're going to get multiple colors, it's usually more cost effective to order a beginner set on Amazon instead of buying the colors individually.  Your student can also use a single color and then paint their model with acrylic paints.  I personally used acrylics to add some details after baking, just for fun!

I use my desk for modeling but for my own kids, I have plastic cafeteria trays in order to keep the clay off the dining room table where we typically do crafts.  In the grand scope of craft supplies, polymer clay isn't especially messy but it can wreck havoc on carpet and upholstery with the right conditions, so plan ahead for where the project will be.  Hair and dirt sticks to the clay easily until it's baked so you'll want to keep it covered between sessions so you don't end up with a furry model.  I personally cover it with a piece of waxed paper and keep it in my room, but modeling on a piece of parchment or waxed paper that can be lifted up and set in a container with a lid is also a great option.

Acrylic paint can be messy and typically doesn't wash out of things, so consider if you want the hassle before deciding to go that route.