Head ; side

1.Researchers found that classical music encouraged people to spend US$40 per meal. The bill comes to US$35 a head when there no music at all.
(a head?)

2.Kaka hopes to play a bigger role as captain of the under-23 side that will take part in 2004 Olympic Games.
(under-23 side? )

A head = each. Per person.
Under 23 side. Not sure about this one. The group that's under 23 years old??