Selective hearing is common at this age lol.
I suggest two approaches. First, give her a Time Call about picking up her toys "You will need to pick up your toys in 5 minutes because we are going to the store." After you tell her to pick up her toys, and if she tells you to do it, remind her they are HER toys, not yours and it's HER responsibility. Don't yell, stay calm and matter-of-fact, even emotionless, about it. Don't get pulled into an emotional battle with her about it. If she won't comply, act confused. "Why on earth would you leave your toys out for someone to step on them [list other possible consequences]."
Second, she will test boundaries. But pick your battles. Instead of fighting with her about the shoes, put a special basket in the car for her to put her discarded shoes into. Encourage her to learn to put them on by herself. If she chooses to go unshod :) I would let her, it's good for foot development.
One more thing. She is technically too young (in most states) for a seatbelt booster. She should still be in a 5-point harness until AT LEAST age 4. She needs to meet the weight, height AND age requirement. PA is not that specific, but I kept my kids in 5-pt harnesses until the age of 5, they are much safer that way. How safe can she be if she can get out like that and make you pull over? That really worries me, she could even CAUSE an accident that way.
this:
"A convertible or front-facing seat with a 5-point harness is the safest option for children from 30-40 pounds who are not too tall for their front-facing carseat."
from here:http://www.car-safety.org/faq.html#Q4