Stair-button rip fence
When I need an accurate rip on a job site without a tablesaw, I use my stair-gauge fixtures. I clamp them on the front and back of my circular-saw baseplate, equidistant from the blade. This requires a saw with a flat baseplate. Measure the distance from the blade to the stair buttons just as you would with a rip fence, and then make the cut normally. With this quick setup, I get tablesaw accuracy.
Gred Gross, Wooster, OH