[¯|_(ツ)_|¯]

Can you start small? For example, it may be difficult to work on EVERY single area of insecurity at one time. Try and find one area that you really want to work on the most and work on that, and then build up to some of the other areas you want to work on. For example, as far as dressing the way you want, you can start with an accessory that you like and eventually build up to a full outfit, one piece of clothing at a time.

I've been told by a lot of people that nobody actually pays attention to what you are doing in public. Everyone is honestly too absorbed with their own stuff and worries. So I bet they won't notice if you're walking quickly, or if you're alone when you eat, or anything like that. In fact it's actually pretty normal to go out to eat!

I'm the same way with public transportation so I feel you on that one. I don't think there's anything wrong with going with other people until you are used to the route yourself and know what to do. The first (and only) time I took a train by myself, I had my friend show me what track to use because I was afraid of getting on the wrong train. But, at least I got there!

I've also had the experience of people paying for me before. One time my card kept declining at Starbucks even though there was money on it, and the lady behind me paid. I bet she's forgotten all about the encounter by now, just like the person who paid for you on the train. They did a kind deed and wouldn't have done it if they didn't genuinely want to help you. I don't think they were mad or upset.

There's also nothing wrong with some of the things you do, like paying with cash in the store. There's no shame in using cash! You're still paying for the item, and that's what counts. And with holding people up in stalls or lines, it can be a mild inconvenience for people but they'll get over it and move on with their lives. You're not going to ruin their day by changing in a stall (I'd change in one too). If that ruins their day, they probably have bigger things going on that have nothing to do with you.

Practicing not worrying does take time. Perhaps you can write a list of reassuring comments in your phone such as "nobody will notice if I do -x-" or "they're just strangers and I'll never see them again" and others. That way you have a reminder when you're worrying that you're not a burden to anyone.