Hi Mashudu,
We know that there are specific standards by which mappings are done between SAP and the POS systems but it always does not happen in the way its suggested. What I mean to say is clients or should I say the consultants do map fields interpreting something else which is away from the standards.
Anyway a good practice is to follow the standard practice and do not alter the mapping. It is better to maintain the bonus buys in such a way that you get the desired results. For instance taking your example if you want that the cost of the bag to be adjusted on the bag as well as on the laptop you could define a % off bonus buy instead of a free goods bonus buy. Likewise you can use other bonus buys to get the desired affect.
An important point to note here is how the POS sends the data back to SAP for e.g. for header level discounts, etc
Regards
Kaizad
