Then you can also ride short everyday-useful trips (grocery store, work commute if applicable, whatever) in regular shoes.

You might also consider fitting a diagonal strap on the no-clip side, like the "Power Grips" Sheldon Brown mentioned just above click-in pedals. I say "like" because the real thing is ridiculously expensive; if you want this, make it yourself out of something like a cheap lashing strap.

Also, of course, the helmet. As Mike says, indispensible. (There is a rather famous English surgeon who says it's no use, but he's talking out of his arse.)