Amazon has this AmazonBasics Bento Lunch Box Containers - Set of 4
For $6.70 as an add on item.
Features & details
4 stackable containers ideal for storing meals
3 individual compartments keep food separated and organized
Larger compartment can fit most sandwiches
Designed with easy-open lids (not leak-proof)
Bento lunch boxes are safe for use in the microwave, freezer, and dishwasher
Made of FDA-approved, high-quality polypropylene
Measures 9.4×6.1×2 inches each (LxWxH)