Very good spec here with little to work with. I had made a few pictures with arrows pointing here and there but then had to go to a meeting and couldn't finish them.

This one:

You can see it isn't a typical wheelbarrow, the legs are not attached to the bucket, they are tipping the bucket up instead of tipping the legs up, so it is easier to put together and take apart.

You can also see a slot in the top of the wheelbarrow.

I think that once it is taken apart they use the legs for one thing and the base for another, or the legs that form the point by the wheel looks like it could fit into that slot. We don't have enough caps to know exactly what yet.

The standing symbols almost seem elemental to me, the round ones being air, the squared off ones being fire, but whether or not they are I'm not sure that matters to this challenge. As Tribe pointed out, none have been altered at this point.

The starting mats seem to be backwards, the Upolu mat is on the right side but the Upolu coconut trough is on the left and vice versa. If they have to start by assembling the wheelbarrow at the mats and race away from the mats and pick up things along the way, then Upolu has the inside track and a shorter distance to get to their trough. The challenge area is quite large, I have drawn an overview:

Usually they will build the challenges to be equal distance, so possibly when leaving the start mats they may have to zig zag to go get whatever they are getting. Or possibly they have the wheelbarrow pieces scattered around the back of the challenge area but they take off from the starting mats in the same direction as my drawing. If they have to collect the pieces and then build the wheelbarrow and then wheel it to the coconut trough to dump the coconuts in, I can see why at this point Savaii seems so far behind.

So what are the coconuts used for once they are in the pit? What if the wheelbarrow bucket is meant to be attached to the platform that K/W/J are standing on and the legs of the wheelbarrow get flipped upside down and the narrow part gets inserted into the slot that we can see. Possibly there are more parts for a rubber sling shot that each person runs out and collects, drops at the assembly area and then they add that to the Y part of the legs now upright.

Then each tribe must shoot the coconuts using the rigged slingshot at the targets to knock them down/break them. This could explain why Mikayla comes back empty handed, they are still gathering the slingshot parts.

In any case, there has got to be something that the coconuts are used for once they are dumped in the pit.

I'm not sure who came first hosting games, you or Tribe, but you are both nefarious! - CTGirl