I was 38w 3d when my twins were delivered....they were a scheduled c-section (blech) and I think that I would have made it to at least 40 weeks if I had had the balls to tell my doctor he was a coward and demanded to be allowed to go into labor (but that's another story.) Baby A, Ava, was 7lbs 6oz, and Baby B, Genevieve, was 6lbs 5oz.
I have no idea why I was able to make it that long. I quit my job extremely early, like around 8 weeks, because I was bleeding, the Xmas season was coming up, and I was managing a retail store, meaning 12+ hours on my feet 6 days a week. I was planning on quitting just a few weeks after that anyway, since my dad had been diagnosed with cancer and his days were pretty numbered.
I spent a lot of time on the couch and I drank a ton of water. I don't know if it helped but it certainly didn't hurt. I was only on bedrest at the very end due to PIH, and even then I got up several times a day to pee, shower, and make myself a sandwich.