We have the caboose. We stuff a bag between a rear yepp seat and use lots of bungie cords, cabener clips for all the extras they bring home from school. I also have some small bags clipped to the bars of the caboose for treats! Before we had the caboose, they just had to wear the back pack.

I was able to order the caboose today. The white RW4 was also available  too.