Here's what I wear and why. Note that I would gladly buy all of it again - everything I wear has been an "upgrade" over the years to my old gear, and I'm now 100% happy with everything. This will be my first season with the 509 Armor vest and Grip gloves, but I'm feeling very good about them.
Helmet - CKX Mission
I love this thing, people make fun of me for how much I love it. It never fogs, even when not plugged in (though there is a heated shield as well), great visibility, very warm, very quiet, adjustable sun viser, and adjustable sunshade. Crystal clear and no glare at night. Super easy to pop the shield open and chat.
Base - Merino wool (various brands / weights)
Depends on the weather, but I always wear a base layer. Sometimes a very thin one, sometimes a thick one. Similar deal with socks, though my socks are almost always thick. I like copper sole thermal max.
Mid - 509 Armor, maybe a sweater / sweatpants if it's really cold
This is my first year wearing chest protection of any kind. Tried a tekvest, just too bulky for me sadly. I'm very worried I'll be too warm with the 509 on warmer days, but I'm crossing my fingers that with the liner pulled from the jacket and no sweatpants, I'll be fine. Since I got my FXR outers (see below), I've never ridden anywhere cold enough to have the jacket liner, a sweater, and sweatpants...but it could happen?
Outer - FXR Renegade FX Jacket and Bib
I much prefer bibs to pants, they make the whole seal with the jacket much better, and they're much easier to wear. The downside is, they're notably warmer, and as you can probably tell I'm never too cold but frequently too hot. I do not wear the jacket liner - I don't think I ever have - I'd occasionally wear a sweater but now that I have my 509 armour, likely not. I LOVE these pants and jacket because a) super warm b) very comfertable c) FAST floatation technology makes me feel better on the lake d) tons of venting for when it gets too hot, especially on the pants. The only downside is that there aren't as many pockets as there could be in the jacket.
Boots - Columbia Bugaboot XTM III
What?! Not a real snowmobile boot?! Heck no. These things are SWEET. Affordable, warm as all hell, very small / lightweight / athletic / supportive, completely waterproof, made by Columbia. Mine are 9 years old right now and I LOVE them (they were the first thing I upgraded over my old gear). They're made for winter hiking, so if you're an athletic rider, they're a perfect match.
Gloves - Skidoo Grip gloves
My hands are the one thing that frequently get way too cold. Rather than constantly chase thicker and warmer gloves, I decided to get a pair of muffs, and the grip gloves. Should be warmer than ever, and also be able to feel the bars way better. Fingers crossed (pun intended) they work as well as I expect them to!