Even easier, and no email trail back to you:
get the phone number for your target restaurant
call them, preferably after a busy meal time, but this works well anytime
explain you are yyy.zzz from abc company, and that <target item> was missing from the order. When they apologize and say you can pick one up, tell them you're sending your son/daughter down to pick it up
then pick up the item, free food!
use a fake name, but REAL company, just not one connected to you
if you are creative, don't be afraid to "ham" it up. A friend of mine who could have been on jerky boys crew used to do most of the calling.
Call to KFC: "Yeah this is John Ruggero at Durable Towing. we picked up our order, but I did not get my chicken sandwich, and Jeff is missing his...what do you call those half-moon shaped thingies..."
KFC: "Potato wedges, sir"
To KFC: "yeah, those.
KFC employee confirms, 1 missing chicken sandwich and one order of potato wedges
To KFC: "sounds good, I'm going to send my son down to pick it up, should he ask for someone down there?"
Usually the answer is no, but make note of the persons name if needed. This is just to let them know to expect a young person to pick these up. Try not to send the same person in to pick up as who makes the call, in case someone recognizes voices.
This above is "advanced". Start with just asking for one item, two is much harder, as two screw-ups are much less likely.
Even more advanced is the no-call. Just walk in and explain the order was messed up and get free food. This is NOT easy to do reliably, especially when you are young. People assume it is a prank/not real. This is why the call works so well, people assume they are speaking with an adult, who is sending a young person to pick up. Speaking from personal experience, you will have much better results sending a girl in for this mission. Our favorite was sending one of the girls in wearing her bikini top and shorts, explaining she was from the strip club down the road and was missing xxx and yyy from the order. Several times we had guys just hand her bags full of food!
I lived off the land, doing things like this, traveling like a gypsy, for months, when I had to
Now that I have some money I like to pay for things