Everyone above seems to be talking databases etc - all a bit techo for me!
There are plenty of "Packing Lists" so the following are more of a few ideas from "out of left field" rather than the obvious tools etc.....
1. A hard, padded, weatherproof camera-case. Soft-padded camera-case wasn't a good idea, I'd rather sacrifice a bit of space for a working camera! (My luxury for myself is a preference for taking a good SLR camera & lenses, if a point-and-shoot is more your style then disregard);
2. One of the "head-nets" - a mosquito net you wear over your head. You look like a bit of a dill - but they are increadibly functional (and scrunch up into about the size of a wine-cork);
3. Less crap, less clothes;
4. A remote control for your camera (Canon make one for their camera's about size of a cigarette and cost about $US20.00);
5. Gaiters and good leather work/hiking boots - far more functional than calf-high riding boots;
6. Maglite and headstrap - I used to use a caving-lamp style, but Maglite make a strap that allows your AA torch to slip into on side of your head. Gives convenience of a good hand-torch and head-lamp arrangement (don't buy it, get wife/girlfriend to sew one up from a cloth scrap! Save $US15.00);
7. Berocca (stomache-ease soluble tablet's) - a luxury I can't do without!
8. Chamois towel - instant drying (squeeze) and a tenth the space of a cloth towel. You just can't wrap it around your waist!
9. A Leatherman and a good Swiss Army Knife (complement each other - what one can't do the other can). If I had to choose one - go for the Leatherman; and
10. Contact-lense cleaner - I don't wear them, but excellent for cleaning lenses, mirrors etc.
Well I hope the above give you a few idea's. None are probably truly essential, but just my experience in making lighter functional loads (hiking trekking background before started riding only a few years ago) and don't seem to appear on mainstream lists.