So far this conversation has implied that backing in and backing out are the only options. Most of the parking lots that I visit offer a third option: pulling through. You don't have to back in or back out when you pull through, but you usually have to spend a few more steps walking between the car and the store. I'm OK with that, because it typically means that I'm not parking tight up against someone with a big SUV that's got a high probability of dinging the side of my car when they open their door.
Responding to Roadkill401
, I know my experience in this respect is ancient, and maybe things work differently today or work differently in Canada, but the last I knew, at least here in the USA, if someone hits you in the rear, the insurance company automatically considers them to be at fault. Meaning, you could rocket out of a parking spot in reverse and if someone hit you behind the rear door, then absent really compelling evidence to the contrary, they are at fault according to the insurance company (in jurisdictions that care about fault).
Which is not to suggest that you want to have this experience, even if someone else has to pay for it. Which is way I prefer to pull through when I can, not have to back out, and not have to rely on RCTA to spare me the headaches of dealing with insurance, body shops, and after effects when the insurance and body shop says you should be great, but something still isn't quite the way it used to be if you ever have the misfortune to be involved in a collision..