in the vehicle - lunch, batteries, spare ammo, spare socks, boots and pants.
on my person/partner - camelback, usually around 20 rounds of ammo - depending on rifle, mouth call, roborabbit, electronic call, bi-pod, ROPE. do not forget ROPE. should not be twine, but a sturdy length of rope depending on the walk you have. Sling, get a good comfortable sling as well. I love my BFG medic on my hunting rifles actually, great for all ways of carry, easily adjustable.