Believe it or not, 50 years ago there were binoculars very close to as good optically as there are now. But they were Porro prisms, not roof prisms. They were somewhat bulkier (though often lighter), and not as waterproof or rugged as some we have now. But many of them got used hard, and the ones that survived aren't as in good shape now, partly because the lens coatings tended to be softer. But they were very fine optically.
I suspect a lot of the stuff on this list so far is there because the people who respond either weren't born yet 50 years ago, or were so young they couldn't afford it, whether really good binoculars, guided hunts, or plane fares. While I'm making a lot more money than I did off my paper route and summer jobs in 1965, with inflation factored in the average household income in the U.S. is just about exactly the same now as it was then.
I did fail to answer part of the original question: What I could not do without on a hunt. Actually I can do without a laser rangefinder, and did part of last fall, just to see what it felt like. I can also get by without a GPS, because I learned to really use a compass and map when younger, but GPS's are quicker and more accurate. The notion that the Barnes TSX changed hunting is interesting, but my wife and i have killed a pile of animals with TSX's and I can't think of one that would have survived or run off wounded because we shot it with any of several other bullets.
Apparently I misunderstood the question somewhat, or didn't really think it through. But I do believe the laser rangefinder has made the biggest overall difference in both hunting and hunting gear, since it not only made it possible to determine the exact range, instead of guessing or estimating with a scope reticle, but changed our scopes, rifles, bullets and general knowledge of external ballistics. And all of that is true even if we, personally, don't use a rangefinder.
