I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot[Flatten /@ Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]]1], Epilog -> {Red, PointSize[Medium], Point /@ Outer[List, x, y]}]] 
ContourPlot[ Interpolation[Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}] 
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot[Flatten /@ Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]]
ContourPlot[ Interpolation[Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot[Flatten /@ Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1], Epilog -> {Red, PointSize[Medium], Point /@ Outer[List, x, y]}]]
ContourPlot[ Interpolation[Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot@ Flatten[ MapThread[ List[Sequence @@ #1, #2]ListContourPlot[Flatten &,/@ Flatten[Transpose[{Outer[List, x, y], mat}, 2]{3, 2, 1}], 1]1]]
ContourPlot[ Interpolation[ FlattenAt[MapThread[List, Interpolation[Flatten[Transpose[{Outer[List, x, y], mat}, 2]{3, List/@2, Range@Length@x]][u1}], 1]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot@ Flatten[ MapThread[ List[Sequence @@ #1, #2] &, {Outer[List, x, y], mat}, 2], 1]
ContourPlot[ Interpolation[ FlattenAt[MapThread[List, {Outer[List,x,y], mat}, 2], List/@ Range@Length@x]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot[Flatten /@ Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]]
ContourPlot[ Interpolation[Flatten[Transpose[{Outer[List, x, y], mat}, {3, 2, 1}], 1]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot@ Flatten[ MapThread[ List[Sequence @@ #1, #2] &, {Outer[List, x, y], mat}, 2], 1]
ContourPlot[ Interpolation[ FlattenAt[MapThread[List, {Outer[List,x,y], mat}, 2], List/@ Range@Length@x]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot@ Flatten[ MapThread[ List[Sequence @@ #1, #2] &, {Outer[List, x, y], mat}, 2], 1]
I don't understand the "combining" part of your question, but this makes a contour plot:
ListContourPlot@ Flatten[ MapThread[ List[Sequence @@ #1, #2] &, {Outer[List, x, y], mat}, 2], 1]
ContourPlot[ Interpolation[ FlattenAt[MapThread[List, {Outer[List,x,y], mat}, 2], List/@ Range@Length@x]][u, v], Evaluate@{u, Sequence @@ ({Min@#, Max@#} &[x])}, Evaluate@{v, Sequence @@ ({Min@#, Max@#} &[y])}]
