1. Define all the materials in your plant (subcontracting and packaging
2. In the material master MRP 4 view there is one field in which you can
mention that this material is not relevant to MRP planning, use this field for
subcontracting material so that it will not be planned in MRP runs ( generally
use this field for re-order point planning).
3. In the BOM for the subcontracting material put the special procurement
key as Subcontracting and do not keep relevance for costing.
4. If you're using packaging material of your company and want to capture
the cost of these materials in the subcontracting production order then put
relevance for cost.
5. Define alternate BOMs for each customer.
6. Generally the routing will be the same but materials will change, define
different prodcution versions for each alternate BOM and assign to the routing.
7. Define the activite types for packing and mixing in the work center and
assign them to the cost center, use these for your routing.
8. Whenever you recive a sub-contracting order, use the relevant production
version depending on the customer.
In my place all the palnts belong to the same client in sap and they want to
use the same material code in both plants, so I think my subcontracting scenario
might be different from yours but it give you some ideas to go about it.