Last week I mentioned that my favorite Korean snack is ggul ggwabeggi. However, I probably should have specified that those honey twists are my favorite convenience store snack.
My absolute favorite street food snack are the cream-filled waffle sandwiches. I usually get strawberry cream, and wow... it is delish! Good thing there isn't a vendor located conveniently near my place; I actually have to make an effort to get one of these waffles -which, incidentally, I never do. But, when I happen upon a stand accidentally as I did this past weekend, all bets are off.
Based on my limited experience, the best vendors are in the subway stations at Sinsadong and Euljiro-1.