The Aus Gov style guide states a transitive verb is when the action of the verb "passes" from the subject to the direct object. That makes no sense.
The man performing the action is a 'subject' and through some unexplained nonsensical magic, the action passes into 'his lunch', when he buys it.
As if the lunch could perform it's own actions, or could receive a man as a subject.
In reality a bag of chips is just an inaminate object and cannot 'host' verbs. The man buying the chips is the source of the verb and retains the ownership of the verb, like wikipedia states.
So did the lunch buy itself?