I use these: http://sprintaquatics.com/prodinfo.asp?number=900
I've used them for years, both on day trips (while hanging out on top of a mountain) and backpacking trips. They weigh about an ounce a piece and are surprisingly durable. I bought several pair assuming they would wear out really quickly, but they have held together a long time. They are pretty thin on the bottom, but still keep out most thorns and little rocks. Occasionally you can get something to poke through, so you do have to watch wear you are going (but not as much as if you walked around barefoot). I slip them on when I need to go to the bathroom late at night and manage just fine without a headlight (which means I'm not being that careful about where I step).
It is a luxury for sure, but a cheap and fairly light one (two ounces for very comfortable feet). I use trail runners, but even sneakers aren't as comfortable as these (I never wear shoes inside my house either). I've thought about adding even more padding on the bottom, which would make them really cushy and not much heavier (an extra half inch of foam doesn't weigh much) but just haven't bothered. Unlike slippers or thongs, they aren't likely to slip off my feet.
Edit: Also, I've thought about combining these with very light slip on nylon "socks". This would make them completely bug and dust proof. I haven't found anything like this, though (Goretex socks would be overkill) — I was thinking of something similar to wind shirt material.
There are different places that sell these, but I would size up. I think I bought size 11-12 (U. S. Men's Large) even though I am a 10.5.