They're not hard to create and you can fill them with what you think is appropriate. I take my time and spread the cost out so that I'm not feeling pinched in the wallet. Most of it comes from the Dollar Tree stores, though sometimes I find a real good deal elsewhere. The bags are those I get from festivals or events (there's almost ALWAYS someone giving those away as a promotion). Some of it, like the hand towels, I'll find in bulk and divide up.
This bag is my "female" bag. I keep meaning to add feminine hygiene to it, but it's otherwise ready to go. It's only "Female" right now as the gloves are pink and the socks are sized for women. Otherwise, it could be for either.
This one is my "male" bag. I found the gloves/cap on sale at Dollar General. The blankets are on sale at Wal-Mart. The rest I bought in bulk at some point and am still dividing up.
They ride in my car 24x7 generally. The only thing I have to watch as to make sure the food doesn't expire. I rarely have the bags in my car long enough for that to happen. If it comes down to it, though, they make great emergency kits to keep in the car as a "just in case".