Create a separate campaign with a low priority, and create 1 product group for all products and assign it a low bid. This optimization recommendation you make to a new client with Shopping campaigns that don’t include all of the products the company sells.
Explanation: In your Shopping campaign, create an ‘All products’ group with a low cost per click (CPC), such as £0.15. This product group helps to make sure that you have full local inventory and local intent query coverage.
Read more here: https://support.google.com/merchants/answer/7232982