The front of my woodworking bench is flat so I can clamp large objects (like doors or table tops) to it for working on their edges or top. 
 
One end of the work piece is clamped on the front clamp, I also have a 4' long tee track embedded into the top front edge for clamping the other end of the workpiece. 
 
Because of the variety of widths/lengths I need a variable way to support these objects.
 
So I came up with this support trestle.
The trestles are 21" long, 6-1/4" high, and 5-1/2" wide with a center support/stiffener.  
 
One problem I faced was the trestles moving around when I had several stacked, so I drilled a 1/2" hole in each diagonal corner of the legs and a mating 1/2" dowell sticking out of the matching top.
 
The dowels sticking out of the top help keep narrow doors / table tops from slipping off one side.
 
 
 
 
|   | Trestle support in use.
 
Here is a 20x36" top for a loading bench being sanded. | 
|   | Trestle stack close up. | 
|   | Trestles stored under my woodworking bench (in purple oval). | 
|   | The alignment hole in the bottom of the foot (Red Circle). | 
|   | The alignment peg in the trestle top. | 
|   | The allignment fit as they are stacked. | 
|   | Yet another pic showing how they are aligned. | 
|   | A pair stacked on top of the WW bench. | 
|   | A closer view showing the wall board screws holding them together. |