You don't not want to pick a specific product until the matching one is also available or want to pick only a specific category. You can exclude/include individual products from this pick or select entire categories to be excluded/included.
To Exclude or Include a product from the pick, click on the product name on the gray band at the top and select [Exclude from Pick] or [Include in Pick]
e.g. if selecting the 'Exclude from Pick' option - The product box is faded and this product is excluded from the pick.
To pick only one specific category click [Selections] > [Exclude Products] > [All]
All products are now excluded
Then click [Selections] > [Include Products] > [By Category]
Select the Category you want to include in this Pick
Products from this Category are now selected
You can add products from another category in the same way and run the pick once ready.