I kept a trunk of costumes, or clothes that could be used for costumes, because my son was more interested in role play than in toys. When he was 9 he auditioned for Henry V at Oklahoma Shakespeare in the Park. He was cast as 'the boy'. He was the boy who died at the end of the play and who was carried away by King Henry as the curtain fell. It was important to me to go every night it ran.
I loved every single performance. Only I couldn't help getting emotional every time the dying scene came. During my son's last performance a twin tailed meteor flew across the sky. I was convinced this was a sign of future acting success, but no such luck.
If it's allowed, take a picnic and adult beverages, a blanket or a low concert chair with a back is ideal. Even in the warmest climates, the night becomes cool, so bring layers to keep warm.