Each group needs:

• 1 ceramagnet (a ceramic magnet made of iron, nicke, or beryllium oxides in clay; available from Sargent-Welch and other companies for ~$5 each)
• 1 compass (small 16 mm compasses are available in packs of 10-12 from various online retailers such as Edmund Scientific at https://www.scientificsonline.com/product/mini-compasses-16mm-pkg12-item--3053606)