plotting – Manipulating a list to make it nested

I have a long list, where the elements are of this kind {x,y,g,a1,a2,a3} and I want to extract some sublists with which I can make plots or manipulate the elements.

For instance, if I want to make a ContourPlot that has x and y as the cartesian axes and g as the “third” axis that creates the contour, I would really love to have my entries rearranged in a nested way as {{x,y},g}, from which I could easily create an InterpolatingFunction like:

newlistTEMP = Interpolation[nestedlist, InterpolationOrder->2];
gfunc[x_,y_] := newlistTEMP[x,y];

However, I am failing at finding a clever way to rearrange the elements of my list into the desired nested list form.
The best I can do is to extract a sublist like:

sublist = Cases[list, {x_, y_, g_, _, _, _} :> {x, y, g}];

but after this I am stuck.

Thank you for your help!