I use public transportation.
There are many benefits to public transit, including that it:

• Is Economical (less than $100/month unlimited rides)
• Doesn’t require me to have to deal with other drivers, traffic, parking, etc.

There are also some less-than-pleasing aspects:

• People with no respect for physical boundaries
• People with no respect for auditory boundaries
• People who are just plain invasive in some way
• People who (ugh!) smell bad
• People on cellphones (too much information, too loud!)

I’ve developed some coping strategies for some of these issues and am still working on others.
My iPod is my primary line of defense for auditory self-care. I don’t want to hear people’s cell phone conversations, I don’t really want to talk to (most) of the people I encounter on public transit (there are one or two notable exceptions) and I don’t want to hear the various coughs, sneezes, and other body noises the people put forth in public places. Ugh!
So the iPod. I have hundreds of songs on my iPod as well as podcasts and audio books. (I love Audible.com!) I just learned to make “on-the-go” playlists. I have a playlist that’s got good rhythms for walking, one that’s got no lyrics (which is good for work listening; I can run my iPod through speakers at my desk), and I even have a moody one which suits my most recent state of mind. I’ll post the contents of some of these lists at some point in another post.
For olfactory self care, I’ve developed a couple of little tricks that work for me. Some people I encounter on my commute wear too much aftershave or perfume. Some smell like stale (or fresh) alcohol or tobacco products. And some have >ahem< real hygiene problems. Smells are a HUGE emotional trigger for me. So what do I do?

• I carry a Vicks menthol inhaler. That blocks the smells and helps my breathing
• I carry a sprig of fresh lavender or rosemary in my pocket. If necessary, I roll the sprig in my hand and that pleasant (to me!) smell overpowers the smell that offends me
• I carry an essential oil or other scented product in a scent I like along with a cotton ball and, if needed, put a drop of the product on the cotton ball and hold on to that for my olfactory pleasure.

The space boundary issue is one I don’t have a good solution for. I mostly try to get window seats and stare out the window and try to block out awareness of anybody sharing my seat. Any ideas from the readers on this one?
And there’s always Rescue Remedy. Don’t leave home without it!