There were yellow cubes that were the cargo boxes, and then blue sort of oblong shapes that were materials bundles (can be either plastic, metal, or rope.) The "collect x cargo boxes" just meant collect the cubes, and it tracks how many you've grabbed in the bottom left corner. Originally the cargo thing was part of a bigger idea I had at the start but quickly realized I wasn't going to have time to flesh it out so I just kinda made the cargo boxes be the mission objectives for now in order to create some kind of gameplay loop for the jam.
I'm glad you enjoyed flying around, and thanks so much for checking it out!