These overmitts:
http://www.aerostich.com/aerostich-t...it-covers.html
Put them on before your insulating gloves get wet and put the gauntlets inside your jacket sleeves.
These booties:
http://www.rei.com/product/725342/su...r-bike-booties
They aren't the warmest, but they are relatively thin and will fit in a jersey pocket.
If it's going to be miserable the whole way, the Only Thing are Lake MTB boots:
http://www.lakecycling.com/footwear.html
On your ankles, you use Bare Drysuit Ankle Seals, these:
http://northeastscubasupply.com/stor...prod_6466.html
or google. They go over the tops of your Lakes and keep water from running down your legs into them. Still, a pair of dry wool socks in a ziplock is always a good idea. This combo is what I wear in the PNW winters (and fall and spring), where 33° and sleeting is not unknown. One ride we went on was so bad that the people who actually finished were riding single-speed because their cassettes were a block of ice with only the one cog clear. We were wise and bailed.
Rainlegs:
http://www.rainlegs.com/en/home
are really, really good in sleet.
So that's how you do it. I should say that there is a thread among randos that says that the more miserable the experience is, the better one is for it. That thread is over-represented on the web. I know a lot more randos who have taken a vow to only have fun and not be miserable again than I know folks who go out for the misery. That said, if one is into ultra racing and loves it then one has already self-selected for the misery part.
The white streaks are graupel.