Update Cart Custom Fields
Carts (Orders) are Element Types and can have custom fields associated with them.
Custom fields can be useful for storing further information about an order that falls outside line item options or notes.
You can update custom fields on a cart by posting data to the update-cart
action.
<form method="post">
{{ csrfInput() }}
{{ hiddenInput('action', 'commerce/cart/update-cart') }}
{{ redirectInput('shop/cart') }}
{{ input('text', 'fields[myFieldHandle]', '') }}
<button>Update Cart</button>
</form>