Re: 4 y old get out of car seat
There are a couple things I would try:
1. Pick a really fun place to go that your daughter wouldn't want to miss (this will work best if she has a friend, sibling or cousin that could also get to go), then right before you go, you say "I'm sorry, but you always unbuckle your seat and get out, so you don't get to go today because that isn't safe. When you start to listen and stay in your seat, you can go next time." Then GO and leave her home. A couple times of this, it WILL work.
2. I'm sure some people are going to have a wig out when I say this, but if you must take her in the car with you and she just refuses to stay buckled, put mittens on her and duct tape her hands together. It won't physically hurt her, don't make a giant fuss about it, just tell her you want her safe and it's the law that she be buckled. Then when you get to your destination, untape her, remove the mittens, again making no fuss. If she throws a tantrum during the drive, do not talk to her, do not cajole or bribe, just get wherever you're going, remove the mittens and go on about your business. She'll get the clue that you're very serious about her safety. You aren't yelling, you aren't spanking, you're keeping her safe.
3. If she gets unbuckled, immediately and safely pull over or off at the nearest exit, get out of the car, tell her she may not be unbuckled in the car, then give her a 4 minute time out right on the side of the road in the parking lot, whatever. Once again, don't argue with her, don't bribe or coddle and don't talk to her during the time out.