Now go through the exercise of "preflighting" the order for all the parts. This is a preview of the Procurement phase. Go through each item in the BOM parts list. If the component is in stock, set it aside in a Parts Kit box. For parts that are not in stock, add them to a Digikey shopping cart, but do not actually place the order. Digikey does a very good job of creating online parts kits for projects, take advantage of it. I must do this before laying out the board, because any change in the physical parts due to cost or availability will completely trash the layout. The layout should be the final design step.