So many things have come in the last 20 years:
Goretex: it's amazing material, and for those of thus that remember vinyl rain gear that only wrestlers who needed to cut weight liked cause you sweated your arse off if it was above 60 deg F.
Chemical hand, toe and feet warmers: my hands and feet turn into ice blocks when the mercury dips below 30 deg F. These wonders make even the coldest weather tolerable.
Cordura nylon over neoprene: Probably has saved many a duck hunter big money with all the holes it prevents in the neoprene.
The 20 gigamillion watt spot lamp: remember when we were working through the maze in the marsh with the old 6V flashlight with a standard mini-bulb?
LED lights: great for the clip-on noggin lamps to keep you from tripping over everything, including the dog, finding things in the duck boat, untying knots in the decoy lines, and great for boat trailer tail lamps.
Cell phones: although I silence mine when I'm afield, it sure does bring piece of mind on those solo ventures (and even the party hunts) knowing that duck hunting is one of the most dangerous of all sporting events due to the dark + boat + water + cold and assuming you keep it dry, can call for help when needed.
So many more, but don't want to keep rambling... Look forward to reading others.