Humm, well tools, food and drink would be #1 on my list.
If the weather looks like it is going to rain, rain gear is a BIG plus as riding in the rain without it isn't all that fun! I strap it down on my passenger seat with another indespensible item... Bungie straps!
I don't know why but it seems like everytime I go out I need my rain suit. Somewhere along the line I usually need the too . Gettin old isn't fun but somebody has to do it.
Live it like you mean it, this ain't no dress rehearsal!
Max
the #1 thing is not physical but metaphysical... like a good attitude. take it everywhere and everything works out... even the seemingly impossible becomes improbable and then all of a sudden it just happens. serendipidty doooo. the more "stuff" you bring is just more baggage which you havent left behind. i've seen lots of people overloaded on trips.