Suggest Items in Cart via Playa relationship

Edit Subject

hey there

i want to use playa to suggest items during the checkout process of my site. i only have one weblog though -products- and each entry will have items that are related to it. normally those products are sorted by category to display throughout the site, but for the "suggested" bit i'd like to implement, i want to be able to suggest specific items not limited to that same category, but that i think someone would like based on their interest in the item they selected.

i'm using cartthrob for the shopping cart, and what i can't wrap my head around is the fact that, on the "cart" page, the url doesn't include an entry_id, and also there will (hopefully!) be many entries in the cart.

in a section below the cart, i'd like to display entries from the products weblog that are related to the item/items in the cart.

EE v1.6.9, Playa 3.0.9, FF 1.4.3

any ideas?