Backyard Cup -
Finish "FANtastic" in the Story Mode and then buy for 210 nuts.
Penny -
Finish level "Try, Try Again" of the Story Mode, and then buy her for
140 nuts.
Stella -
Finish level "Depelter Turbo" of the Story Mode, and then buy her for 70
nuts.
Sound Test -
Finish the "Ozzie's Trek" level of the Story Mode.