What materials do I need to install pantry shelving?
Unsupported 1x12 over a 5' span will sag (even under its own weight).  As an alternative you could get some of these shelf tracks (~$2.25/track)

and some 12&quot; brackets (~$1.30/brace)

and then lay your 1x12's on top to make the shelves.  This option also allows you to easily adjust the shelves up and down, to suit your needs.
If you want to make the shelves completely from wood (as you suggest), you'll need to beef up the design and add additional supports.