He fell from the sky
The package contained a radioactive isotope and his going out into the field was to distance himself from the populace to ensure their safety. Eventually the radiation came to be too much and he succumbed to the poisoning.
Makes sense in my head.
Wait, not even his own footprints?
If that is the case, then I am guessing he fell out of a FedEx plane and one of the packages that it was carrying fell out with him. He knew he was going to die because he was falling through the air and the ground was quickly approaching him.
This isn't an original question.... I reckon I heard this about 20 years ago.
If I recall correctly, the unopened package is his failed parachute.
My guess is he fell from a plane. This does happen as I can recall two stowaways falling from the sky a few years ago. They obviously had died of exposure and when the wheels opened to come into landing there bodies fell out. The package next to the body is what he was carrying as his belongings.
A psychic told him he would be put in a great predicament where he had to deliver a package, otherwise his entire family would be brutally slaughtered - yet he would die of a heart attack on his way to deliver it, and his family would still be saved.
Thus, he sacrificed himself for his family, dying of a heart attack he was forewarned of.
He was having a heart attack.