affix solar panels to the front of a normal messenger bag , with a flap over top to hide them when nessecary. you can probably buy wiring and small solar panels off the internet. that's...about all i know. buttt...with all the money you'd spend/the chance of wrecking it and having to start over, it might be easier and cheaper to just buy that bag instead.
instead of packing tape, use clear vinyl. durable/waterproof. make panels by arranging your cards evenly spaced on a sheet of vinyl, sew the other one on top, grid-style. leave an inch for sewing-together space, you know the drill. then you could either make a fabric stap by just sewing it unto the inch or so of tarot-free vinyl on the top edge, or cut the tarot cards in half and make them into straps using the vinyl method. if you do use packing tape, put it on the front and back. the tarot cards will be ruined otherwise. hope i helped.