I wear these neoprene and rubber winter boots. They are 2 sizes too big to accomodate shoes or extra socks with warmers. Although these have worked well, my feet still get cold even if its only -15C. Mine are purple for the cuteness factor which is also very important. My teenagers would say that I am very much mistaken and that they are not at all cute. I am planning to put the galoshes over these.
It took a year for me to break down and buy disposable heat packs. It makes me crazy to generate this much waste. However, there doesn't seem to be a way around this one and they are good in emergencies. I used these in the Kamiks and they have saved my feet. They are supposed to work for up to 20 hours. A nice hint from the pros is that if you haven't used them up, store them in a plastic bag and remove the air. The absence of air makes them stop working so that you can use the same ones again!
Best to go with a screw top water bottle because the sippie part of the regular water bottles will freeze up ( I lack the technical term , but you know what I mean). It is for this reason that I experimented with gatorade ice cubes. If only I had known....
Even this will eventually freeze up in an insulator so another tip is to invert the water bottle so the ice will form first at the bottom instead of the top. The pros say to take a sip every 15 minutes even though you won't want to.
It really is possible to ride your bike in the winter and it is fun too!