Wiring a combination switch/GFCI outlet with lightswitch downstream
Based on the diagram so far, here's how the GFCI switch/outlet combo should be wired:


Black from breaker to LINE HOT on GFCI/switch
White from breaker to LINE WHITE on GFCI/switch
White from switch-cable and white from light nutted together and pigtailed to LOAD WHITE on GFCI/switch
Black from switch-cable and one black from GFCI/switch nutted together and pigtailed to LOAD HOT on GFCI/switch
Other black from GFCI/switch nutted to black from light


(If your GFCI has the two-wire, clamp-plate terminals as in the diagram depicted, you can save a couple nuts and the pigtail wires by terminating both wires to the clamp plate instead -- they are designed to terminate two wires, one in each hole.)