Coupons.

1) I've never done this, but it would be possible to build an add-in to do it. I've seen this at supermarkets, and they usually print coupons off a separate printer - that seems like a really good idea, and should probably be included if you wanted to pursue a custom solution.

2) You can use Item Messages to do this, but creating the Item Messages and linking them to the proper items could be unwieldy if you want to suggest add-ons for many items. This could also be improved upon through add-in, and could even be related to the coupon generator of your first question.

I'm not aware of any add-ins that address your questions, but there may be something out there. Building add-ins to order is generally expensive, but if you business requires this functionality, it can be created.