A toy wagon usually refers to a load or a burden you are carrying around with you. The fact that the wagon is a toy may suggest that you are handling the situation immaturely or aren’t being adult enough about it. Depending on the context of the dream – and what happened the day before the dream – it may even mean you NEED to play and have fun in order to lighten your emotional load.
A pioneer wagon may suggest that you are paving the way for others. Are you embarking on a new journey? Are you creating something new? Are you venturing into new territory?