Understand what products to bundle, how many to include and the price your customers are willing to pay.
Questions you could ask:
"If you were in the market for this product, how many would you order at a time (if the per item price was cheaper)?"
"How much would you pay for this product bundle that comes with 3 28oz bottles?"
"Would you be more inclined to purchase this product if it came with a travel size as well?"