Plywood is a great building material. It is strong, dimensionally stable, and is available in large sheets, up to 4' x 8'.
That last benefit is also a problem for most of us woodworkers, since we are often working alone and it is unsafe to wrestle a 4x8 sheet of plywood over the table saw, at least without the aid of a couple partners or the judicious use of infeed and outfeed tables.
The one-person solution is to reverse the situation. Instead of moving the wood over the blade, move the blade over the wood! Just use a guide of some sort to ensure a straight cut. This allows you to cut plywood, MDF, particle board, or any other large panel down to size with accuracy that approaches that of dedicated panel cutter machines.
And the best part of all? It is made from scrap lumber - birch plywood offcuts or old glue-ups!
The choice of blade is between a jig saw and circular saw. Now the jig saw has a narrow blade and it is designed to allow for tight curves, but it does allow for straight lines when the occasion arises. The problem is that the rate of cut offered by the jig saw is rather limiting when a large number of cuts is desired. Also, the small blade and reciprocating action does not lend itself to the smoothest cuts. And using a blade with more teeth (offering a smoother cut) slows the jig saw down to a crawl.
The circular saw, on the other hand, has a large blade that acts as a rudder as the cut is made through the wood, and its rotary action holds the blade in a perfect line once the blade is spinning.
The jig is essentially a narrow plywood board glued to a wider plywood board. The trick is that the wider plywood board is not trimmed to any particular width until AFTER the narrow board is firmy glued in place. After glueup, the circular saw is run along the jig, with its side snug against the narrow rail which acts as a straight-edge, and the circular saw cuts the wide board to the exact width of the circular saw's base.
For the top piece, ensure it is straight and true along its narrow edge, since it will act as a straightedge for your circular saw. Also, select a piece that is wider than your circular saw's motor, since it simplifies clamping the jig to panels.
Because this jig will be used on fine wood, knock off the sharp edges with a bit of light sanding on the corners. The faces of my jig did not need any attention since they were made of scrap birch plywood with good faces. I also like to apply a coating of wax to the top side of the plywood since this will ease the running of my circular saw.
Using the jig is as simple as using a ruler. First support the panel. Remember that the panel ends will separate, so each end must be well supported so they do not fall once you have made your cut. If the cut piece is allowed to fall, it may tear the surface wood, and leave an unsightly blemish that will be hard to hide.
Place the jig along your panel with the edge of the jig precisely on the line that you want to cut and clamp the jig in place. Remember that the blade will remove the wood right up to the jig, so mark your lines and setup the jig appropriately. If your circular saw body threatens to hit your clamps as you run it along the jig, adjust the blade height so that saw body is raised. Just make sure there is enough blade in the wood to cut through in one pass!
Then place the circular saw on the jig, start the blade, and start your cut. Be careful as you approach the far end of your cut because unless you are as tall as I am, you will probably be leaning or reaching. DON'T. Stop the blade and slide back the jigsaw an inch or two, move to the other side of the panel, then continue the cut from the other side. The following sequence of images demonstrates the action.
Still haven't gotten enough? Here's a helpful YouTube video of a similar jig in action.