A while back I designed and made a leather field belt for my geologist girlfriend. I had the best leatherworker I know teach me, and it is actually super fun. It includes a rock pick holster (quick-draw), a field notebook with space pen and pencil, a leatherman & holster, and a loupe with a holster.
Take an oversized piece and soak it in water for a few hours, then nail it down with BRASS tacks as tight as you can around the object you want it formed to. In this case, I used a wood block so I didnt ruin the book.