Below is a list of how to reach 100% completion, and what everything in the game is worth (by percentage).
* Ninety Story/Procedural Missions - 68%
* Acquire each friend's special ability and do their activities - 10%
* Win at each activity and mini-game - 5%
* Find all random characters and complete their missions - 5%
* Kill all thirty wanted persons - 2.5%
* Complete all twenty vigilante crimes - 2.5%
* Complete all fifty stunt jumps - 2.5%
* Eliminate all two-hundred pigeons - 2.5%
* Complete all thirty car thefts - 2%