Within your product database, there are likely to be many items that if associated together, would encourage the customer to purchase multiple items when normally they would have taken only one.
Similar (i.e. shampoos from other brands), related (e.g. the conditioner to accompany a shampoo) and alternative (i.e. a comparable product to choose should this one be unavailable) associations can be created, that not only help the customer to navigate your products, but also encourage higher expenditure.
