I use old fashioned pen and paper.

I have a weekly calendar, one column for each day and it is 8.5x11 landscape. I plot out my week with things like errands, standard weekly things like "put out the garbage", "pick up co-op share", etc. Add in work tasks, etc. Cross off when done. Circle when not finished.

I also have a "shit list" as it is entitled. Tasks here need to get completed or bad things happen :-)

So I carry around a few pieces of paper and my trusty pen.