The crystal things in the box... possible spoiler

They were glass candles that didn't light up, they were for decorative purposes only. His father had various failed jobs as salesman trying to support his family, and this was one of them. Earlier in the film there is a scene where Aaron was invited to a rich classmates (Billy) home, and his mother was driving them in her fancy car. At a stop sign, she spots a salesman she recognized, and said, "Look Billy, there's that salesman I told you about. Why anybody would want to buy a candle that doesn't light?" Unbeknownst to her, she was making a remark about Aaron's father. Aaron got embarrased at this, and sank lower into his seat.

Appararently Aaron was smashiing the glass candles up because he was angry at his father for leaving him all alone, and the candles were just another one of his failed ventures.

If only Aaron, who is always so quick-witted and well spoken, had thought to say, “They are decorative candles for warm weather entertaining, when it’s too hot for flames. Only rich people can afford them.”