Every Block in Unicorn has a 'Block Targeting' setting, which enables you to only show (or not show) the block when specific items are in cart.
You can set this up by collection, product tag or product item.
So if you want to show a specific 'Cross Sell' item when certain items are in their cart, then this is how you would set this up.
You can also have multiple cross sell blocks in your cart with a trigger to display when certain items are in the cart.
You can label the Cross Sells within the cart like this (just edit the name)
Then at the bottom of the block, in block targeting, set the cross-sell to appear for specific items:
Then when that item is added to cart, the cross-sell block appears:
If you have another item with a specific cross-sell, you can set them up in the cart blocks and the offers will stack if both items are in cart at the same time:
