You could use something like these:

{{!gwi}}

But you may need to increase the material thickness to accept the bolt. Biscuits might work too. In any case you'll want to make sure the shelves are supported in the area of the joint.

Just putting a cleat that spans the joint under your shelf at each joint may be the quick and easy way to get things done. Glue and screw.

Just make a but joint and glue the shelves together.

Adding biscuits or even dowels can help with alignment during glue up, but the glue will be stronger than the wood itself if you have the correct even thin film of glue with an otherwise tight joint.

If you use plywood for the shelves you can have a single piece with no joints at all up to the size of the plywood sheets.

3/8 thick AC plywood with a hardwood edging on the perimeter (about 1 inch by 1/2 inch edging) makes adequately stiff shelves for most uses.
I put the edging under the shelf on the back ad above the shelf on the front to keep things from falling off while preserving as much shelf space as possible.

If you use hardwood for uprights they only need to be about 1 inch x 1 inch.
You can fasten them to drywall using Wall Dog type screws and just build everything in place.

Watch out for out of flat walls in the corner from drywall mud.

You can carve some of the mud away to clear the edge banding.

The last pantry I did had 'U' shaped shelves 4 feet wide, 2 feet deep with a 12 inch deep x 2 feet wide cutout to make the 'U.'

1 inch x 1 inch verticals (4 along the back wall, 4 along the front, nothing on the inside shelf corners).

The final touch was 3 low voltage puck lights (20 w each) on the ceiling with a door operated switch and 24 VAC relay.
The relay wiring is all standard HVAC control stuff (transformer and relay) and switches the 120 V side of the AC to DC supply for the pucks.

The pucks are on a piece of 1x4 on the ceiling mounted against the door wall.

This post was edited by brickeyee on Wed, May 15, 13 at 11:31

Thanks for the detailed suggestions. The dimensions are 94 x 44, so I could use one sheet of plywood for each level (for the entire L), but that would only use about 24% of each sheet area. It would also require that I Planning something in the 9 to 12 width along the 94" side, with about 16" on the other side.

Lighting is from a 4' 4-tube t8 fixture.

But joints should be fine if you use the edging as long as possible on each side of the joint.

Put a very small rabbet on the edging (like 1/16 inch) an increase the dimension of the thickness by that amount.

So instead of 1 inch x 1/2 inch edging, make 1 inch by 9/16 thick, then cut the rabbet 3/8 x 1/16 deep.

Making the edging self aligning on the plywood with that small rabbet makes glue up a lot easier.

I still have a bunch of panels since I used a router pattern to make each shelf.
Two shelves from each end of an sheet of plywood leaving the center of the two 'U's as a single larger piece.

A few have already been used for other things.

This post was edited by brickeyee on Wed, May 15, 13 at 14:53

"A few have already been used for other things. "

If I had been thinking about these earlier, I'm sure my cabinet maker could have used much of the extra material, assuming I used the same 3/4" plywood as he used for the boxes. He still may be willing to take some of that off my hands -- 3 box sides would consume about % of what is left after I cut out my "L" shelves from the sheet.

3/4 ply is likely to be overkill for pantry shelves, unless you plan on stocking a lot of #1 (institutional size) cans or want to omit edging.

That little bit of hardwood edging ads a lot of strength to the shelves.

i used ash for the past few, and they do not sag more than a few hundredths of an inch when loaded with all cans in the worst spot (I had to set up a dial indicator to measure even that).

Try and bend a piece of 1 inch x 1/2 inch ash a few feet long.

Hope OP doesnt mind if I intrude here - but would your edging suggestion (Brick) work on kitchen cabinet mdf shelves that are already sagging slightly? No institutional cans but I do have stacks of heavy china. Have been trying to think of a way to beef up those shelves

The edging should help by stiffening the shelf.

It will be even better if you can attach the ends of the edging to something solid.

Even a 1/4 inch thick piece on the back of a face frame for the edging to rest on at each end.