You have to win the indicated events to unlock the corresponding bonuses:
Boots:
Golden: European Cup
Green: Portuguese First Division
Orange: Dutch First Division
Red: French First Division
Silver: EURO Cup (UEFA cup)
White: German Cup
Shirts:
Codemasters: English League
Guerrilla: Portuguese Second Division
Home & Away: Spanish Second Division
Lederhosen: German Second Division
Showtime: Dutch Second Division
Tartan: Scots League
Tropical: African Cup
Tuxedo: Italian B Division
"I Love Sensi": French Second Division
Hair:
Afro: German Shield
Aging rocker: Portuguese Cup
Bouffant: Super Cup
Monk spot: French League Cup
Mullet: English Shield
Rasta: Dutch League Cup
Receding: Scots League Cup
String band hair accessory: Italian Shield
Ponytail: Spanish Shield
Footballs:
All-star ball: Italian Cup
Bright yellow ball: Spanish Cup
Classic old leather football: English Cup
Retro black and white ball: German First Division
Tournament ball: South American Cup
Pitch types:
Snowy: Italian A Div
Icy: European Cup
Muddy: English Premiership
Synthetic: World Cup
Carpet: Spanish Premier League
Shorts:
Guerrilla: Portuguese League Cup
Hearts: French Cup
Kinky: Dutch Cup
Leather: Italian League Cup
Lederhosen: German League Cup
Tartan: Scottish Cup
Tropical: Asian Cup
Trunks: Spanish League Cup
Union jack: English League Cup