My "day" hunts are typically in remote country with at least a fair chance of an unexpected overnight.

Obviously good navigation bits- compass, map (usually printed off the computer via Caltopo) and a gps (my iPhone w/ Gaiagps app)
I bring an inReach Mini with and always leave a detailed as possible itinerary w/ my better half for communication.
For shelter I carry an Apex quilt, it has a "poncho" hood so does double duty as a insulating layer when glassing for very long; a short section (~50") of ccf pad- doubles as a sit pad; and a SOL Escape bivy, Silky Saw- helps construct a shelter, firewood, etc, but I carry a bone blade with it as well- these items would mean a miserable night out, but one that I would survive
Fire kit- a pretty bombproof kit that in addition to normal fire bits (lighter, sparker, reliable tinder)- a small flare and two packs of Trioxane.
First aid kit- more full stocked than what I use for "summer" backpacking that includes items for major trauma that are normally not carried.
Water is usually carried in wide mouth Nalgene as I can worry less about freezing, than other bottles- a half dozen Aquatabs.
Additional clothing- a mid-layer, an insulating layer, if it's early season- a rain jacket, heavy fleece mitts, heavy fleece balaclava
Food- usually a dozen bars (200-ish calories/per), a pretty large lunch- the most I eat on the bars is usually six, the other six are there just in case
Kill kit- two knives (one a replacement blade knife w/ extra blades), small sharpener, bags, 100' of cord, marking ribbon, a 3x6' of Tyvek to process meat (this also doubles as a groundcloth if needed), two pairs gloves, licenses & tape
Headlamp - two headlamps w/ a set of spare batteries, I take two headlamps as they are used almost every hunt- going in and coming out
around my neck I wear a lanyard with a Photon light and a whistle (signaling)

all fits in a 20 liter pack smile