Just got my first deer kill last night after my 2nd year of hunting (Got skunked the first year, but wasting disease pretty much wiped out the local population so I don't feel too terrible). Here's what I would recommend.
First, understand that deer do what they want. I know that's not an equipment thing, but seriously, they're pretty unpredictable. Here's why it's relevant.
Opening day a nice doe came by, about 80-100 yards out. It's a long shot for me (Shotgun with irons), but I had a nice broadside shot and I took it. I missed completely. With that first shot, the doe whipped around and sprinted back the way she came across a field. I took another shot on the run (In hindsight I probably shouldn't have) and missed again completely. Normally I'm a decent shot, but all of my previous experience had been shooting at paper. Once the deer was in my sights my heart was just a yammering and I couldn't keep that shotgun steady to save my life.
Anyway, back to the point. Couple of days later a couple of yearlings came out. 30 yards away tops, broadside shot. They were little guys and the property owner asked me to only take bigger ones because the locals wanted the population to recover. Because they sat their feeding for 20 minutes (again, beautiful broadside) I texted the owner what he thought (He was in binoc distance). Well, instead of texting me he calls and my cell phone blows up (although I swear on all that is holy I muted it). Dang deer didn't even look in my direction. Ended up letting those go.
Last night was the end of gun season and pretty much my last chance. I'm sitting in the blind reading when I caught movement out of the corner of my eye. Two nice does trotting across the field from behind me. I whip up the shotgun and, again, miss completely. I'm not even sure I remembered to aim. Anyway, both does literally froze, giving me a nice second shot. This time I calmed down and took the shot, dropping on of them where it stood (Ok, so I still shot high DESPITE aiming, hit the spine - sigh). The other doe just stood there. It continued to stand there when I stood up and started walking to my kill (Keep in mind this was maybe 30-40 yards tops). THEN it decided to move on, but it kind of trotted 15 yards away and then stood still again. Sure wish I had a 2nd tag.
Here's what I got from that.
1) Load up the full mag. Sure, the first shot is probably the best, but if I didn't have the extra rounds available I would have missed out on my kill.
2) Bring something to do. I found reading a book would keep me out there an extra hour or two and anything that I would miss between reading pages I wasn't going to be able to hit anyway. Just remember to keep glancing up.
3) I'd probably put hearing protection on ahead of time and just leave it on. I've got electronic muffs but the battery started go by the end of the night so I had one ear covered and one half-covered. Never crossed my mind to drop the headset down over my other ear and I might not have had time to anyway given the deer were at a trot.
4) However much clothing you think is enough, throw on an extra layer. I was out one weekend when it was about 2 degrees and brought a wool blanket with me - worked great to keep me warm although I'll admit it was cumbersome.
5) Cleaning the deer is a hot mess. Bring TWO knives because you'll probably find one gets dull, especially if you're trying to get through bone. I would also bring a pair of rubber dish gloves. It's not that it's gross, it's that it sticks to your hands like nobody's business and water doesn't do a great job cleaning it. Plastic bags to throw the soiled stuff into is probably smart too.
6) A tarp so you don't soil you vehicle works great.
7) I liked having a pair of binoculars, but they're more for amusement than anything practical. Anything I needed to look through them to identify I wasn't going to hit anyway.
8) A flashlight for when you're cleaning your deer after sunset because you're like me and have no idea what you're doing.
9) I'd throw in a compass if you're going into the boonies. I was in a farmer's field so I never needed it.