Take what you honestly think you will use. The first year I hauled around more "might need" items than stuff I really used.
If you forgot something, there is a Wal-Mart in the next town.
My only exceptions are, my tool box, a small air compressor and the tools needed to change my TT tires.
They can make the difference between a twenty minute inconvenience and sitting until Road Service can find you on some back road. That is assuming you have cell service to call.
My experience is, if you forgot what to need, you will remember it the next time.