You poor thing it sounds like you have your hands full. From what you are saying it seems as though you are doing everything right..

And yes, he occasionally does the refusing to get into the trolley or the carseat, I usually have a few "bribes" up my sleeve such as a toy hidden in the car that I can produce to distract him long enough to strap him in, or I start talking about how we are going to get his favourite fruit when I'm approaching the trolley.
Along the lines of what I was going to say. DD1 is 99% good but a few times I have had some tantrums that just don't end. I have found she seems to like knowing what we are doing and what we will be doing next. I tell her we are going home and that we will be playing outside, cleaning up (she is a regular 'Sadie') ect. And if I just start singing she normally stops straight away. I know what works for us wont work for everyone, but it is just a couple of suggestions.

I think our LO all go through periods of change and really push our limits, but it wont last forever. My SIL attended a 123magic course and had great success from it, that might be something you could look into.

Goodluck hun, I hope some more ladies can come with some great advice for you.