You can either directly query them from the list, or take the more verbose route through the items:
document.list('shopping_list').required_string_values # Note the plural here document.list('shopping_list').items.map(&:required_string_value)
An important gotcha here is that in the shortcut version required string values does not mean there have to be items in the list, but only that items need to have a value. If you look at the non-shortcut version this is obvious, but for the shortcut version it's important to keep in mind.
optional_* variant of this accessor produces the less commonly needed array that might contain
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