You could build a table of products_id and products_id_to_add
When a products_id gets added to the cart, it checks if the products_id_to_add is there ... if not toss that in there too ...
Pehaps expand it to know should it add in the same quantity or different quantity ...
What to do if first products_id is removed, if anything ...
What to do if the customer says no way ... how to avoid readding ...
Or do it the smart way ... have it display the suggested products based on what is in the cart for the customer to then add to the cart themselves and not upset the customer with all these products that they did not add suddenly showing up in the cart and making them scared and causing them to run off with their credit card to another site ... :eek: