Back to the main approach, simplest way and probably the quickest:- A body (drinks can and drinks bottles usually) and an unbalanced motor - shaking its way around. The vibration makes the junkbot move but it is not controllable.
The 'homemade' nature of creating wheels and axles, and without direct drive usually lead to the junkbots based around wheels not moving easily (it was different when wheeled toys were used instead). Homemade 'legs' though did often work.
Here are some examples:
The second used a tripod arrangement of legs.
Remember though – keep the weight down, extra decoration is fun but usually lead to slower junkbots (or in some cases stationary junkbots).