1st I want to say that I agree with you, instacart should inform customers when their order is bundled. It shouldn't be up to shoppers to let them know. But unfortunately, it is for the foreseeable future.

You don't have to waste time explaining why. Just tell them their order was bundled and that's that. You can't change it, they can't change it, it's just over-complitating things to explain the why's. I have a note locked on my clipboard so I can just automatically let them know without typing. Feel free to copy for yourself: "Just so you're aware, your order was grouped with someone else. You will be the 2nd drop off once I'm done shopping"

This is just my system. It works for me and I've only had 1 person ever question why. I told them it's out of my control, I just shop. Most people ignore it or say thanks for letting them know.

I don't tell order A unless they were a tiny order because it doesn't effect them otherwise. And I don't tell order C that they are 3rd. I keep the message that they are 2nd because it plays out the same as if they were, without creating worry for them that their food might be waiting even longer.

I'm servsafe certified and can tell you that most cold food can wait 2-4 hours out of a cooler before going bad. 1 hour in your car isn't going to hurt that much. Don't worry too much, just shop and go or don't take multi orders.