Whilst it is possible to claim damages if you can show that the takeaway owner owed you a duty of care, and that the damage to your car/clothes was forseeable, my view is that a claim against the takeaway owners would not succeed.
Whilst they should have ensured that the containes was properly secured and should have forseen that if it was not, then some damage could occur, the takeaway owners would claim that you contributed to the damage through your own negligence.
Most people (myself included) realise that there is a risk that some sauce/food/grease etc can escape from these food containers. They are not foolproof. Therefore you should have been able to have forseen that there was a risk of some spillage and you could have minimised that risk by placing the bag/containers within another bag, or stored it in a place where spillage would not cause any damage. So I think that if you ever did take this to a small claims court the costs/damages would at best be split.
Personally I keep my takeaway food in a plastic box in the boot of the car, or occasionally, in the rear footwell of the car. Never, ever, on my seat....just in case.