Speaking as a buyer, if an item doesn't have a price tag on it, I will very seldom ask how much it is...I just keep going to the next yard sale. So even though it's a pain, I think it's better to take the time to price everything.
I haven't had a yard sale in a few years, but I tried to group things by price when possible. For example, I had a big rack of clothes and put up a big sign that said $1 per item. Or, for a box of books, I would do a sign that said 25 cents each, etc, etc.
I like the idea of using separate sheets of paper and sticking the original sticky price tags on it. Write down the things that didn't have a price tag. I've never done a multi-family yard sale, but this sounds like a good way to keep track.
I agree about selling drinks...you'll make a killing, even if you buy generic pop and Huggie drinks for the kids. I've seen people sell Rice Krispie treats before, and they sold like hotcakes.