Two spare silicone o-rings - especially for the old(glossy lid) b.box sippy cup. To replace o-ring, preferably using b.box's straw brush cleaner tip, or similarly rounded tool, carefully slide tool around ring's edge (in between plastic lid and silicone ring) until raised and able to remove. Then, securely insert the new o-ring into place. Dishwasher safe. Made from silicone. BPA, Phthalates and PVC free.