Two of the most tedious backpack sewing tasks are making pre-stretched elastic pocket rims and inserting foam into shoulder straps. The videos below show techniques I’ve worked out using simple tools you probably already have at home. There may be better ways or better equipment to do these things, but the techniques below seem to provide consistent results:
Pre-stretched elastic pocket rim:
https://youtu.be/e4qHGPUmKy4
Shoulder strap foam insertion:
https://youtu.be/9j_9Fjoe3gg
For the elastic rims, I use 3/4″ elastic band folded in half and then sew it to the pocket mesh using a zigzag stitch. For the foam insertion guide, I use heavy construction paper with the outside face completely covered in clear packing tape to make it slick.

