Well, I'm not vending as I have a joint in the back of the local general store, but I would recommend a few ads in local papers - especially if you have a Penny Saver/Shopper style paper. We have something here called The County Shopper - basically a classified paper with local display ads. We ran a few "Bring this ad get a free drink" with great response. People reading those sort of papers - & a lot of people do - actually also read the ads.
As you're vending in the snow, might I suggest our motto "Seasonal BBQ is for wimps". Make the trailer in the snow thang & plus not a minus for people. Put some picnic tables up. Make some tables out of snow. Have a snow man contest.
Also I'd suggest dropping menus off at local businesses. Does not take a great deal of money to have some run off at Staples or Office Max. Put some on the trailer for folks to take with them.
Finally - use Facebook/Twitter/website. I know you may think people in your area are not interested, but you'll be surprised. We use our website & Facebook page to let folks know our specials & whether we've sold out of anything. Had about 50% of NYE orders come from people reading our menu on our website. Do not underestimate the power of the web - especially when it comes to vending Q.
Much luck. I'll be thinking of you as I light my smokers on (compared to Boise) balmy -5º Catskill February mornings.
Cha Cha Hut BBQ : 43311 Route 28 (corner of Route 28 & County Road 38: Arkville, NY : [URL="http://chachahut.com"]chachahut.com[/URL]
Backwoods Pro Jr.
busted Backwoods Fatboy
Weber 22.5 Kettle
some stainless wood fired thing