For backcountry riding and sometimes trail riding, i carry a shovel, sno bungee, gps, platbooks/maps, water, a couple samitches, extra oil, gloves, maybe a pair of socks, in my backpack. You will almost always see me with one even if just trail riding, as me and my wife leave the truck in ironwood and ride from there for the weekend. We just drive till we hit the snow then ride from there. Why put the miles on the truck when you can put them on the sled!
My new sleds have almost no storage so they are really nice to have. I used to make fun of the guys who wore back packs till i was out riding with a buddy and we stopped in the middile of nowhere and he whips out a whole buffet of food and drink and nice dry socks while Im sitting there nawing on a frozen snickers. It looks silly but man is it nice to have all that crap with out riding especially if you have one of the back packs designed for snowmobiling and you cant even tell you have them on. As far as standing up, i usually only do that when its rough, off trail or trying to cool off, otherwise i agree you look like and idiot going down a flat trail standing!