First, take your BOM and turn it into a combined BOM + packing list. It should have the part designator, the part description, manufacturer and part numbers, and the quantity used per board. There should also be a column indicating how many pieces you are sending in. (Side note: whenever possible, provide a slight overage of parts -- the extra parts are useful for rework, and the leader on the tape is useful for loading up the pick-and-place machines.) Each line item on your BOM should be in a separate bag. When you order parts from some distributors like Digikey, you can specify the customer reference number for the part. This is a convenient way to have each part bagged and labeled with the reference designator. (BTW, if you generate your own internal part numbers, you can use that instead -- your BOM should then have a column showing those part numbers.) Cross check all the parts you are sending against your BOM. Double check the part number and reference designators. If necessary, relabel bags to match the BOM, as your board assembly people will be cross-checking on their end, and any errors will lead to delays and confusion. Make sure your BOM also lists the PWB (or PWB panels) that you are sending in, too, if you are supplying the boards to the assembly house. Note that the MCU (U1) for this order is already pre-programmed. If you are building hundreds of units, having the chip pre-programmed by the distributor is a very cost effective and time-saving thing to do (adds less than 25 cents per unit in volume).