I ran across this super idea on
2 Excited Nests, a blog written by two sisters who got married within 4 months of each other and now share a blog.
At one of their weddings, they had a basket of
Old Navy flip flops (check out the 2 pairs for $2.50 ones). The guests in high heels could pop these on at the reception and have a comfy fun time on the dance floor.