Make sure to match bulb and battery voltages. Generator lights don't work well in wet or snowy conditions and often don't give enough light at slow winter speeds. The less sophisticated ones give no light when you're not moving. Systems that power the taillight and headlight from the same battery may leave you invisible from the rear if a wire breaks without your knowing it. Independent rear flashers are very reliable and can run for at least a year on 2 AA cells.
Reflectors are available as vests, straps, tape and plastic pieces that mount to bicycles.
When the bike starts going sideways, make small corrections rather than oversteering and weaving down the trail. On some soft trails, higher speeds take less effort than lower speeds, because your tires sink into the snow less at higher speed. Snow machines leave the center of the trail soft. Their best tracks are left by their skis, if you can ride straight enough to use them. Dogsleds leave harder, smoother trails than snow machines.