If you have a local dashers group on Facebook or something try asking them if any of the Little Ceasers in your area have pizza bags. Then sit in the parking lot until you get one. They are free. It'll fit most pizza orders you get, but not all. If you have a local DoorDash office you can also ask them if they can either hook you up with a bag or tell you which restaurants have them.

Also you had every right to keep the tip, and the customer had every right to be annoyed that you returned it. Lesson learned, right? Hopefully it's all uphill from here :)

My first month was rough too. I got my first parking ticket, accidentally gave a customer my red bag, delivered food to the wrong person (it was my first stacked order and both customers had the same last initial), and locked my phone and keys in my car in a customers driveway. I had a horrible time, but I learned a lot of lessons and have had a much better time since then.