I started by sketching out ideas for what I wanted to put in the bento boxes. I knew I wanted to go for a retro Y2K style, so I kept that in mind while sketching.
I designed the bento box layout in Adobe Illustrator, then I brought in and iterated my sketch designs until I felt the style was consistent across the board.
Once I was happy with the designs, I brought the final styleboard into Adobe After Effects for the final polish and animation.