Things like throwing the car could be testing boundries or because he is bored/fed up or a combination of both. Either way, it's obviously behaviour you need to stop.
I would probably take it away and say 'I've had to take it away because you are throwing it and it will get broken/damage the floor'. At that age, I would probably give it back after a short time but say if it was thrown again it will be gone properly.
Sonetimes telling them what you DO want them to do can be more effective, so 'why don't we see how fast your car goes in the kitchen / lets race these two cars'. At the point of him starting to throw, you may be able to intervene and set up a new game, play it with him for 5 mins then tell him you'll be back soon and get on with what you need to do.
Him starting to throw might be his way of asking for attention, remember bad attention is better than no attention (I don't mean you don't give him enough attention). Just sometimes if you can work out the reason for the behaviour, it makes it easier to solve.
When mine used to start throwing, I used to get them to throw soft balls, get them to hit the cushions with something soft or do some rough play-it seemed to get the throwing 'out of them'.
If you can't always get out, look up ideas for indoor things-obstacle course with cushions/mats on floor (jumping between / around them), make a game out of star jumps, hopping, etc or dance to music.
With the dinner, I would maybe take his plate straight away when he started to eat like that. If he wanted it back say he can but he has to eat nicely. If he doesn't then it's gone properly. When you give it back you might have to distract so 'oooh DS, remenber XXXX today, wasn't it funny when XXXX'.
Again, is it his way of telling you he is full up or is he fed up. Do you sit with him eating dinner? I know mine eat much better when I am talking to them/we're doing little games at table. I can't always be botherered though, sometimes I just want to zone out and eat my own dinner. That's when they are more likely to start bickering/messing about though.
There is no right or wrong though, everyone does things differently and different children respond to different things. I think it's just about finding what works for you.