During the introduction sequence, hold Start to unlock all tracks.
During the introduction sequence, press A, B, A, Up, Down, Y, Left, X to unlock the Humvee and Ambulance.
To achieve lots of Kudos in just one race do the following. Go to a Hotlap round, a round in which you only need to beat a lap time, not one of the average time, and start the race. On the first lap, get the time. You now have passed the stage, but do not end the second lap. Find a good, straight portion of road. You get kudos for turning with the handbrake. Go to one side of the road as fast as you can. As you are approaching, do a 180º turn using the handbrake, If done correctly, "Wey Hey" should appear on the screen. Next, drive the way you are facing to the other side and do the same. When moving the wrong way, you need to spin 180º in order to get the kudos. Just keep repeating this, then race normally and finish the race. For every five minutes that you do this, you will get approximately 1000 Kudos. There is no time limit. The best city for doing this is San Francisco, as it has wide roads. Play jokers to get more points -- if you do this for 20 minutes with a joker, you can get more than 8000 Kudos in just one race.
To easily complete chapters in challenge mode, just pull handbrake turns (press A + Left or Right) when going into a corner. If done correctly, the words "Way Hay" should appear. Keep doing this on most corners. but remember to complete the objective as well. When the race is done you will stack up the points.