Mrs. Hutchinson's apron represents the normality of life - she was doing the dishes and "clean forgot what day it was..." The implication there is that Jackson misleads us into thinking that the lottery is important, but that Mrs. Hutchinson was excited to get down to the square. However, normal life happens both before and after the lottery.
The slips of paper are reminicient of a death certificate, to me. The paper represents death, as does the black spot. Black often represents death and the heavy, dark spot, indicates the person to be sacrificed, which is certain death. Black is mentioned also in regards to the black box where the slips of paper are placed - this reminds me of a casket/coffin. It contains death.
Old Man Warner is the old timer - hence the name. He brags that he's lived through so many lotteries and that there's always been a lottery - there's no need or reason to change it, according to him. He's set in his ways.
The village square is discussed as being the place for gatherings - square dances and other things. The village square traditionally (pardon the word choice) is where all important business and fun is conducted. Again, Jackson misleads us with her description of the village square as a beautiful, happy place - and we come to find out that it's a bloody, grotesque place wearing a facade.