I have the Picker little red book, moleskins and a host of other notebooks and pens but I rarely used them - through pure laziness! Then I bought one of those adaptors that converts my iPod to a voice recorder. It works well for me.
I often go out to look for photo ops, (because, for me anyway,there's nothing worse than just "going out to take photographs" without any idea what I'm looking for.) I take the GPS and the iPod and as I spot possibilities I make "notes". This way I build a book of things to be done, and can also work out what time of day, what season, even what weather conditions etc makes the most sense for that subject.
Been out of operation for the past year, so I've had to content myself with building a "To-Do Portfolio" This seems to work well for me.