I'd definitely agree that laser rangefinders have changed hunting, or the way people hunt, the most in the last 50 years. But to the original question, "What could you not do with out on a Hunt" - nothing that was developed in the last 50 years.
A .30-06 with a 4X scope was what I started with, a compass to set a landmark to work towards, a canteen, a sharp knife and a drag rope worked then and would still work now (although dragging would be a lot tougher than it was a few decades ago!). A 4X scope with 7 MOA subtension can tell you all you need to know about range - the animal is in range or the animal is not in range.
Some things developed in the last 50 years have certainly made life easier and more comfortable, bullet development lets one use a lighter kicking rifle with equal lethality, lighter warm and water proof clothing is nice, but there's nothing that is essential.
IMO the one thing that has absolutely ruined more hunting territory than anything else is the widespread use of ATV's - I'm sure that will get a flaming.
