I have some sight pixiepotter. In my case, I am extra vigilant about childproofing the house (more vigilant certainly than most people I know).
I used reins with my first two DC. I haven't used them with my third, mainly because she is usually in the pushchair for journeys like the school run as we are on a time-constraint and can't dawdle.
I keep physical contact with them when possible (arm on shoulder, that type of thing)
I tend to avoid very busy/crowded places - for example we go to the playground early in the day when it's quiet, rather than later on when it's crowded and easier to lose sight of a child.
I train my DC to be road-aware, to walk sensibly beside me/the pram on the school run, to stop at every road, and to check driveways for incoming/outcoming cars. I don't let them run/scoot ahead. I also train them to pay attention to my voice and come when I call them.
I talk to my DC a lot, so in situations where I can't see them clearly, I am aware of where they are from the sound of their voices. They are also used to me saying 'what are you doing', and telling me. 2yo DC3 is endearingly honest e.g. 'I am SCRIBBLING on DS2's PICTURE, Mummy'.
I have perfected the 'goosestep' maneouvre for putting a sleeping baby in a cot in a dark room. Baby in arms, high-kick goosesteps till my foot/leg locates the side of the cot, then lean over and ease child in 