I'm not entirely sure what you mean by volume share and value share, but I'll take a stab.
For volume share I'm assuming you want share of volume (rather than unit share). To get this, multiply each SKU in your simulation by it's pack size and then repercentage to that the numerator of the share calculation is the total volume in standardized units shown. For example if you are simulating and A, B and C have shares of 10%, 30% and 60%, respectively and pack sizes of 100 count, 50 count and 12 count then the total volume would be (100*0.10)+(50*0.30)+(12*0.60) or 32.2 and the volume share of A would be 10/32.2 or 31%. You could do a similar calculation where price replaced unit count for your value share (or share of dollars).
I'm following your lead that you did a standard CBC here. If you ran a volumetric CBC (one where respondents could choose an open-ended number of units rather than picking one of your CBC alternatives) then the calculations could be different.