I have this old pantry cupboard that I am re-building, and I decided to add
thick doors that will hold cans and small boxes. The front of the doors will
have panels matching the rest of the kitchen. (old pine)

I'm kind of designing and building as I go... it's a real hobby for me!

I decided to use fiber board for the partitions, as you can see in the photos.

Any advice on holding all this together would be appreciated! I would like the
option to move things around and change sizes if necessary... I was thinking of
maybe dowel pegs that can be un-plugged, but that sounds difficult to match up.

Also, how to keep the cans from falling out but not using a lot of room - thin
brass straps or something?

Right now everything is an experiment!