Hmmm. I was going to be all organised and ready by 34 weeks. But I broke my foot, and that put a spanner in the works (and I wasn't really organised well enough before that anyway ;)). So when I went into labour at 35 weeks, our bags were only sort of half packed. The baby bag was ready, thank goodness, but the rest of it wasn't. I would NOT recommend it!!! Trying to pack during labour was not fun, especially with my waters leaking everywhere. I was very lucky I had my lists to work from, otherwise I would have forgotten stuff for sure. And as we were 45 minutes from the hospital, and DH was staying with me, we didn't want to forget stuff, because that would mean sending someone else to our place to get it.
So.....I would say there's no such thing as too early. Pack your bags as soon as you feel like it! ;)