Something that has worked for us has been distraction. I usually ignore the behavior and say something like, "Hey look, there's a bird in the tree, what do birds say?" Here are some other examples:
If he won't get in the bath: Get in the bath yourself and say, "Wow, this is so much fun! Oh my! Silly me! I forgot to take off my clothes. Hurry, let's see who can take off their clothes the fastest!" Of course, you don't take your clothes off, but perhaps he will start to take his off.
If he won't get in the car: Say, "That's okay, I can fit in your carseat!" Start to get in the car through the back door, that will send him into fits of laughter! OR say, "Oh my goodness, I can't seem to remember how to buckle your carseat, do you think you can help me?"
If he wants a snack or toy at the store: Say,"Me too, me too! I am so hungry or I love that toy too, but we are not getting a snack or toy today, let's see how many grocery carts we can count?"
If he won't go to bed: Say, "Can you please read me a book tonight, I am way too tired, I would love it if I could just lay here right in your bed and go to sleep!"
These ideas will help to distract your son and get his attention on to something more fun! Life is supposed to be fun and memorable! Make memories with your son, be silly and enjoy life. Show him that there is no time in your schedule for silly fits, fun comes first! I don't know if this has worked for anyone else, but it has on my two children and the many other children I have cared for in my childcare career! Have fun and good luck!