That is a good question and you can really see the answers change from those who routinely hunt late season weather and those who don't.
1) pack- an uncomfortable backpacking or day pack can take a toll on your patience and persistence of an animal.
2) boots- if you cannot hike to the animal you will never kill the animal
3) clothes- although multiple layers for some for early season nothing beats a pair of Tiburon pants for hiking in the heat
4) rangefinder - bow hunting 90% of the time. Trying to estimate distance in the woods with angle cuts is not for me
5) water bladder - I like to drink and will go through 100oz bladder easy. Although most all hunters use one it beats a bottle any day.