Depending on the weather for the day, long johns suck. I always bring them, but rarely wear them. It can be very cold in the mornings and evenings and hot as hell in the afternoon. I prefer to dress in layers that are easily taken off and put back on. If it is going to be cold all day then I will wear long johns. Nothing worse than hiking all afternoon in the heat and not being able to pull your long johns off.

Don't go cheap on the rain gear. You will rarely need it, but cheap rain gear is cheap rain gear and if you need it you will really need it. Try to find rain gear that will roll up small to stay in your pack all day but is a good enough quality to do the job right.