There is more than one way to handle this. I didn't completely understand your process - so this is more discussion than answer.
It sounds like the 'raw materials' you talk about are actually finished widgets that just need to be packed.
I am guessing that the 'warehouse transfer' process was chosen to help in reconciling the 'raw material' inventory and account for the items that are 'missing' while at the packer.
The packing fee should probably be a 'service item' - other charge items are thinks that go below the first subtotal on an invoice.
You are using 'assembly item' which is good. That probably means you have QB Premier (or Enterprise) - which also means you should access to use 'multiple units of measure'. Look for this option. But how to use it depends on how you like to count your inventory. If you count and sell by the case - then 'case of widgets' does need to become its own separate assembly item. But if you tally the total widgets within all the different cartons then 'MUoE' is the way to go.
For separate items then the first assembly should be 1 raw widget + 1 pouch + 1 packing fee = 1 packaged widget. Second assembly (if no MUoE) would be +10 packed widget = 1 case (final sales item)
Not sure how 'item receipt' come into this - unless you are actually recording the assembly as a vendor purchase? Thats a different alternate QB path that bypasses the first assembly.
Any inventory and assembly items should have both Count and Value records in Inventory (unless theres no stock). Valuation is always zero sounds wrong - but im unclear.