In an email, I had suggested to @Miggy that some leftover wood would make a fine bumper. He, in turn, enquired what sort of bumper design I had in mind. Rather than explain, I figured it was easier to build and photograph one... 
Materials:
1 ea) straight track, in this case O27.
2 ea) 2-56 screws and nuts
4 ea) 2-56 washers
Strip basswood (in this case, 3/8 x 3/16)
Using an appropriate sized drill, drill a second hole in the tie (if needed; some tracks have two holes).
Cut two pieces of wood to fit between the rails.
Using the tie as a guide, cut additional lengths of wood.
Clamp, drill and assemble.
The finished product.
This particular version is designed to stop regular rolling stock without hitting the coupler. You can, of course, add layers to make trolley bumpers or whatever.
The design can also be adapted to pretty much any three rail track.
Approximate cost: 25¢ worth of wood and hardware.
Have fun!
Mitch
