The operative word here is "probably." You've picked up the order, driven safely to the customers home, dropped it at their door, petted the dog and (by the way) got paid a Nice fat tip for only going a few miles. Your customer was very good to you. And you were very good to them. You think...
You make it a few miles away when you see that 312 area code calling your phone. That's right, it's the customer or the company...and they aren't calling you to tell you what a great job you did.
Before you answer, your eyes dart around to the cupholders to see if you forgot a drink. Nope. Perhaps a cookie or a coleslaw container escaped an unsecured bag and is lying on the floorboard. Nah.
Did you double check the address number on the house? Was it drive or circle? Are you sure? Quick, can you remember it? Of course you can! You did your best. You have a high customer satisfaction rating. Did you put the order where the customer can see it through the side pane window of the door? Yes you did. You didn't ring the bell because of the crazy dogs like the customer asked. What else could you have done?
The answer is, "not much." You process all these questions in seconds and then answer the dreaded call. The customer informs you that they're missing the hot pepper infused apricot salsa side they ordered.
What can you do about it? Nothing. You could go back to the restaurant and fight with them over it but in my experience the restaurant can and usually will refuse to give it to you.
You didn't forget it. As delivery drivers You can only do so much with a sealed bag full of food. You can show the order on the phone to the restaurant worker but there's little else you can do to make sure all sides are in the bag.
Restaurants use different packing methods and various containers to pack food and it's impossible for you to go through, and in some cases - recognize some dishes.
The only thing you can do is to refer to the sealed bag and indicate to the customer that you can't and don't open sealed items, nor would they want you to. I always ask for some sort of tape or seal so I can point to the chain of custody and make sure they customer understands. This works for almost all customers.
It is your job to make sure the customer gets their food in a timely manner, as hot (or cold) and fresh as possible. Safely, and courteously. Customers will understand that you don't cook or pack the food if you gently remind them. Remember this and offer this slight ex[planation that your customers will understand and keep getting those high customer satisfaction numbers.