I delivered this tonight to my daughter's boss.  Her son's first birthday is tomorrow.  She sent me a photo of a cake she liked and this is what I came up with for her.

The tractor is made of RKT covered with ganache then fondant.  The top tier is white cake and iced with buttercream to look like a bale of straw.  The bottom tier is chocolate cake and iced with buttercream and decorated with fondant.  The family has a pig farm hence the pigs.  I also made a jumbo cupcake and iced it like a bale of straw for the smash cake.

She was quite pleased with it.

I think the next time I would downsize the tractor a little.

This is the picture she gave to me to go by.  Not sure where she found it.

This is too cute! What tip did you use to pipe the hay, and when you say you covered the RKT in ganache, did you crumb coat first and then pour the ganache on? TIA 

Thank you both for your comments.

The tip I used for the hay was a leaf tip #352.

I packed the rice krispie treats firmly into a 4 1/2" x 2"  square cake pan filled to the top and trimmed even with the pan and allowed it to dry then cut it into the pieces I needed.  I used the extra for the tires.  I covered the pieces with the ganache applying it like icing and smoothed it with a hot icing knife.  I then covered it with the fondant which can be a little tricky.

Myra 

I think you did a great job.  The hay looks really good.

Thank you for responding. That's a good idea to let the RKT set in the pan like that - I'm going to try this technique sometime :)