Display custom product field in cart
You could set a variable to access the products model like so:

{% set product = item.purchasable.product %}

and then access the fields like normal {{ product.myCustomField }}

The snapshot holds the products fields as they were at the time the line item was added to the cart. So depending on how you're using the fields would dictate the method used. 

You could also access the snapshot slightly cleaner using 
{{ item.snapshot.product.myCustomField }}