In our setting we have not implemented PP but we have implemented MM and SD. Our products are in our material master....
We would like to take several of our products, kit them together into another product (already in the material master), sell the kit, and have all of this accurately reflected in inventory.
I'm making an assumption here based on your comment that you say "product" that you're talking about your finish good products sold to your customer base. AND, the fact that you've implemented the SD module I making a further assumption that you using SAP's shipping functionality within SD??
Further, since your not on any other module at the present time, you must be doing your financials in your legacy system, inventory for piece parts are in legacy (but inventory for the finish goods are in SAP!!) and your MRP is running in legacy.
This was also our design 5 years ago when we went live with SD only. We had our finish good product in SAP and all else was in our legacy systems. We interfaced MRP demand at the finish good level over to our legacy where "net requirements" came over to legacy to drive our legacy MRP and the manufacturing plan.
You must be getting the cost of your finish good into your financials somehow prior to shipping it out. The way we accomplished this was that we set up an SAP production order at the finish good level only and then replicated this production order in legacy.
To accommodate the scenario that you described above, you can issue out you other finished product out of your SAP stock using a 261 movement. You have to had gone live with some material movements as you need the 601 (post goods issue resulting from shipping) and some others to get the inventory into SAP so that you can begin the shipping process of creating delivery, picking and post goods issue. So you're material movement 261 could be used to "issue out" these other finished products to your legacy job number OR legacy production order in order to capture the cost of ALL products going into now another new product.
Use a 262 material movement OR a production order receipt, a 101 material movement, to get this new product back into SAP unrestricted stock or sales order stock if that's in your design.
Once this new "combined product" part number is in stock (and making the assumption that this is the part number on your SD sales order line item) you can create delivery, pick and post goods issue.