I worked as a courier on cargo bikes. Lots of food delivery apps need catering orders delivered, offices will order a ton of food for meetings ect. You can talk to the the apps and they will set you up with these orders. Also those premade meals like blue apron we made a lot of money from just doing last mile. Talk to local farmers markets and bakery's ect. Look for places that care about being green. Also you could get a job with a proper courier company and use your cargo bike and the dispatcher will keep you full up as long as your fast.
I also really love omnium style cargo bikes they can cut through traffic much faster and are way easier to store in a house ect. They can handle oversized loads really well, useful for lumber ect, but don't do as well with really heavy loads, like children or wood stoves. Look into omniums or any short jawn as well!