R key - Restart the race. P key - Pause. X key - Exit the game. Use the 'rescue' key if you crash and can't get back onto the track. TinyTux will lift your cart up and put it back onto the track.
Bad things happen immediately - and last for a few seconds before 'going away' by themselves.
Missiles - unguided but fast. If they hit anything, they explode impressively. The effect on a Kart is to stop it dead - so you have to accellerate again. They ricochet off the sides of the track and only explode when they hit a Kart. Magnets - if you activate a magnet then it hangs around for about 15 seconds.