At those temps? I'm wearing most of it! For spares I'll have my real winter gloves, another puffy jacket, a hat, more buffs, and more chemical heat packs stashed in my frame bag, saddle bag, or poagies. I have a spare tube, plugs, pump, and tools... but I'm not going to futz around with trying to put a tube in at those temps unless I absolutely have too. No one wants to be touching -30* liquid tubeless sealant, you'll get really bad frostburns from it unless you are careful.
Those -30f rides on my head I'm typically wearing a my helmet, a buff as a headband, a neck buff pulled up over my ears and face/nose. I run fairly warm, so this is sufficient to keep my head and face comfy. That spare buff in my pack is for if I have to hike it out I have a dry layer to put on.
On my top, it's a patagonia mid weight capeline long sleeve, Rab longsleeve hoody, Black Diamond First Light Puffy jacket, and a Patagonia insulated biking vest (totally spacing on whatever it's called). The Rab hoodie is a new one this season, I discovered that it really helps with adding another layer to keep moisture further away from my skin. Usually wearing a pair of Handup Cold Weather Gloves inside of my Dogwood Designs insulated poagies.
On the bottoms, Patagonia mtb liner, Swix insulated shorts, Montane Guide Pro?somethingsomething insulated soft shell pants (these things are discontinued but are a freaking magical layer that works so well for a huge range of temps. I've not found a similar replacement yet). Merino wool socks, chemical toe warmers, and 45nrth wolvhammer boots.
The best thing to do at those temps? Ride with a friend. Picture from last year November, it was -34f when we were out there.
The dog has two coats, booties, and chemical heat packs in hidden pockets of the coats. She's a beast.