You don't have to necessarily make the bowls out of fired clay. You could use airdry clay or Fimo for instance. You could also make coil baskets or handmade paper bowls. I have also seen bowls made that are crocheted and then coated/dipped in a medium which gives them stiffness. I recently saw where recycled magazines were used to make bowls. Perhaps googling images of non-traditional materials for bowls would expand you and your students' ideas about the possibilities. I know that last year in my town there was an art exhibit for empty bowls and most of the bowls were not ceramic!
These are some interesting themes. Perhaps giving yourself some time to percolate or marinate the ideas will give you some additional inspiration. Also perhaps brainstorming with your students may take you all in some new directions in terms of how to interpret the themes or what possible materials you could use to express your ideas. This is the perfect think outside the box moment for you and your students! We're artists and we are facilitating our students in developing their creativity!
My kitchen is stocked with basics like rice, pasta, and beans. Depending on what's in season I can continually update what I prepare. In terms of your art class....if it's stocked with some basic supplies and you supplement with a few specialty items like specialty decorative papers, freebies such as old magazines and other recylables, and donated odds and ends your students will have a "pantry" to stoke the fires of their creativity!