I think the bottled water/soda idea is fabulous - buy in bulk at warehouse prices and sell for $1 or $2, if the weather is hot you will sell out.
I quit advertising in my local paper and stuck to Craig's List and signs. A couple of years ago I did a little survey at my garage sale and not one person came because of the newspaper ad. I had a few who came from CL, but the majority (probably 85%) saw my signs on the street and followed them. I used wood sandwich boards, similar to the "open house" ones realtors use. Got hot pink paper, printed an arrow and "garage sale" in all caps at something like 600 pt font. I taped the signs on both sides of the sandwich boards. I made 4 or 5 of those signs and had TONS of people tell me they just followed the signs. Now whenever the neighbors have a garage sale, they all come over to borrow my sandwich boards, lol!