Immobilizing your hand/arm is a bad, bad idea. This could cause spread and increase your RSD symptoms as well.

If you're hypersensitive to changes in your environment, it's best to limit your exposure to places you can't control. If going out in public sets your pain off and it takes you days to get back to baseline, then try to prioritize what is worth going out for.

It's hard to give tips or tricks when we all react so differently to different stimuli.

Do vibrations bother you? I always use a pillow in the car when I go more than about 5 miles from home. I chose a car that has great suspension.

If I have to wear long sleeves due to the cold, I usually wear a Lidocaine patch.

If an environment is too loud, I'll leave. If I'm forced to stay, I'll find the quietest spot possible or use headphones with calming music. I rarely go out to eat, but when I do I avoid places with televisions, because the flashing lights set me off. And--I choose time periods that have low activity. Lunch after 2pm, Dinner before 5pm. Etc.

I do most of my shopping online now.

I hire people or have family to help me do things I'm no longer able to...

I use my hand and arm for short periods several times a day to maintain my range of motion and muscle. It's even in "normal" ranges unless I flare. I often cook in stages for example.