Winter gear is very dependent on how high and how long you plan to go in the backcountry. On a high peak deep in the Sierra, I recommend a bag rated at lower than 10F. Camp is your safe haven when things get nasty. If you sleep warm and really want to be in your insulation layers
Tent - I prefer a bombproof tent. I have two for winter, both the same design. Mountain Hardwear EV3 and EV2, which in my book are a 2 and a 1 person tent you can live in. Easy to set up with the poles outside. Great ventilation, and once pitched there's no flapping even in a 50mph wind. Whitney tested, both of them. Overkill during nice nights, fantastic to have when the wind wants to sweep you off the mountain.
Boots for me depend on the distance to be covered. Short and steep, I like my Dynafit Mountain TLT5 touring boots, which are super light for a ski boot, walk as good as a classic plastic mountaineering boot, and take crampons like a champ. Plus, you can step in your ski and move at speed. I don't know if I'd like them with snow shoes. I never figured out what boots work well with snow shoes, except maybe those northern trapper type insulated arctic boots, which in turn are useless when you need to put on crampons. For mixed rock and snow travel in the Sierra, I have a pair of La Sportiva boots, yellow with insulation layer and stiff soles compared to my red summer GTX Evos, forgot the name. Work ok if you slop enough waterproofing on the leather, but for longer trips, I'd need to get something more water resistant. The type of boot that works in that category and stays dry is rather expensive - $500 and up, and so far I haven't really seen the need for it, as on longer winter trips I would be on ski that require the touring boots.
Insulation layers - more layers are good, but you want one that's warmer than the typical 5 ounce fill insulation layer,and hooded if possible. Below that there is only one thing for me - merino base layers and a heavier merino sweater.
Pants - I have some Mammut technical softshell pants (current version of it is called "Base Jump Touring Pants"), zipper vents on the legs, stretchy Schoeller fabric, built-in gaiters, etc - love it. Used it for everything from skiing to winter bicycle commuting. Get too warm in the Sierra sun, just open the zippers. Not totally waterproof when you sit on wet snow on the ski lift all day, but for normal backcountry travel where you can sit on a pad, I'd take it any day. Any similar piece of gear will work.
For really cold deep winter trips, I'd consider my hardshell pants (I have some Arcteryx and with Patagonia Nanopuff pants underneath, but that's more for the Wisconsin -20F snowshoe trips, not for the Sierra.
Gloves - you need good gloves when it gets cold. I have about 5 different sets I use for skiing and other winter activities. The warmest are some slightly larger than needed Mountain Hardwear touring gloves. Extra liner gloves from Burton make them super toasty. When it gets even colder, pop open a set of chemical hand warmer packs and stuff them in.
Lots of other special considerations for winter travel - the stove needs to be able to melt snow and not sink into the ground, the hiking/ski poles need real snow baskets, the backpack needs to be bigger, googles, facemask or buff, etc