The system could conceivably learn what a particular user means by "pork" (which cut, how much) and "brown rice" on the first iteration, and then default to that next time if no further specification is given.
The next time, the user has learnt the flow and starts walking down the taxonomy path for pork by asking for "pork"- or so the user thinks! Alexa just immediately dispatches the same cut the user bought three weeks ago. User never trusts Alexa again.
Obviously Alexa wouldn't just order it right away. It could easily say:
> Alexa: "Would like like to order the same x cut from last time?"
[Yes/No]
> Alexa: "Okay great, the total will be x and the delivery estimate is 1hr, shall I submit this order?"
[Yes/No]
> Alexa: "The order has been submitted, I'll notify you when it's marked as out for delivery"
No, I think I want the one from 3 times ago? Or was it 4?
It'd be great for chicken where I usually get the same thing (~5lbs chicken thighs). For beef though it'd be an absolute nightmare. I vary between flank, eye of round, ribeye, rib roast (which granted is basically a really big ribeye) and chuck in different amounts depending on what I feel like cooking.
I also know myself well enough to know I'm going to have a forgetful moment in the kitchen, order "beef" when I'm focusing on something else, and accidentally end up with 5 lbs of flank when I wanted 1 lb of ribeye.