Crash Nitro Kart

Unlock Characters
Dingodile: Acquire Red Gem (Get Red gem Cup)
Polar: Acquire Blue Gem (Get Blue gem Cup)
Zam: Acquire Purple Gem (Get Purple gem Cup)
Zem: Acquire Green Gem (Get Green gem Cup)
Pura: Do 50 or more boosts in a row in any track in Team Bandicoot
Fake Crash: Do 50 or more boosts in a row in any track in Team Cortex
Dr. N. Tropy: Beat all his timetrial records
Velo: Earn 2 scepters

Unlock Movies
Do the following tasks to unlock the movies in the Extra menu

As Team Bandicoot

Challenging Krunk: Get three trophies.
Krunk Loses: Get one key.
Challenging Nash: Get six trophies.
Nash Loses: Get two keys.
Challenging Norm: Get nine trophies.
Norm Loses: Get three keys.
Challenging Geary: Get twelve trophies.
Geary Loses: Get four keys.
Challenging Velo: Get four keys.
Losing to Velo: Get four keys.
Defeat Velo without 100%: Get four keys.
Defeat Velo with 100%: Get four keys, thirteen Relics, and one Scepter.

As Team Cortex

Challenging Krunk: Get three trophies.
Krunk Loses: Get one key.
Challenging Nash: Get six trophies.
Nash Loses: Get two keys.
Challenging Norm: Get nine trophies.
Norm Loses: Get three keys.
Challenging Geary: Get twelve trophies.
Geary Loses: Get four keys.
Challenging Velo: Get four keys.
Losing to Velo: Get four keys.
Defeat Velo without 100 %: Get four keys.
Defeat Velo with 100 %: Get four keys, have 13 relics, and one Scepter.

To unlock Arena Editor
You can redesine the multi player arena's, by beating the "capture the crystle" in the adventure.(When you want to play them, click on custom arena).

How to beat Krunk
As soon as you get 3 trophies, you can race Krunk. When you are racing him, Krunk will drop spikes. If you hit one, jump as much as you can. Then successfully beat him and you will get a key and a cutscene.

CNK Inferno Island
If you're finding it hard to get the C on Inferno Island, at the beginning of the race, be sure to get a super boost, and the veer to the right after the first bridge, and there is a ledge which you must get on top of to get to the C. You must use a slide boost to get a small boost to help get you enough speed to ramp the dirt mound onto the ledge. After making it to the ledge just keep driving until you see the C, then time your jump just right and you'll get it.