What are some ogies to help define/explain reflection, refraction and diffraction of waves?

Whatever you have stated are very good ogies but to generate a straight wave/ pulse, take water in a try and lift the tray a little bit from one side. if water is filled in tray to different heights by raising the floor midway between the edges, refraction can be nicely demonstrated. Also you can take a pair of wheels connected by an axel from a toy car and slide/roll it at an angle towards the boundary of a smooth and rough surface. the turning of the system as its first wheel touches the boundary can be spectacularly seen.