Electrical failure?

So, I stopped at the gas station to get something to drink, as I was about to exit the gas station parking lot my truck shuts off. I turned the key back so I could try it started again. When I turned my key and tried cranking it over, I lost all power. No dash lights, no inside lights, no headlights, not even brake lights when I pushed on the brake pedal. no power anywhere at all. I checked the battery and the battery was fine it had plenty of juice. I checked the wires to both the alternator and starter they all seem to be connected and fine. Could you please help me in trying to resolve this, it is the only vehicle I have? I have two little boys who just started school their first year and I am a single father and also work a full-time job.