On the site I manage we sell accommodations using HB but also other items, such as tickets to events. It would be good to be able to sell different kinds of items in the same transaction, but HB Woocommerce does not allow this.
In HB Woocommerce this is handled by the function preventAddToCartProductWithoutPayment in woocommerce-helper.php, which throws an exception if you try to add another item to the Woocommerce cart it there already is a room reservation.
I wonder why? By removing the exception it is perfectly possible to purchase both an accommodation and another item in the same transaction. But there must be a reason you have made this choice. Is it unsafe to remove the exception?