Adding a multicheckbox in a store product

Forgive me if this has been already discussed, I have a client who would like a product option where the customer selects more than one option via a multicheckbox . I have looked at this page, https://support.wix.com/en/article/adding-and-setting-up-a-checkbox but it is not clear how it can be used in a product scenario?
She wants customers to choose for instance two days of the week for one product, three days of the week for another , so in one simple multicheckbox option on the product… It’s for delivering lunch boxes, her not wanting the restaurant app as she has them as product subscriptions…
Thanks in advance!