Other than filters and fuses.
Or take with you on long rides.
Headlight, J box, etc?

On a trip, J-Box, TCU(Ignitor), halogen headlight in case the HID dies.

On a trip, spare bulbs, minimalist additional tool kit with a 12mm hex key for the front axle.


At home, fork seals and wipers, brake pads, at least one set of serviceable tires, and a pile of misc parts I've collected through the years.


Rick

All under the seat (and stuffed behind the tail light)-
Spare headlight for HID fix
Complete socket set broken into small zipper bags
Reversible screw driver, pliers, small wire cutters, adjustable wrench
Roll of electric tape, razor blades, Exacto
2-12mm allens for front wheel
fold-up allen tool
Small bag containing extra bolts & nuts, screws, zip-ties, wire, other bulbs
A few shop rag.

In top box-
Reading glasses
Tire plug kit
More shop rags
Cord and a few bungees
Large socket for rear wheel
Cell phone charger with splitter to plug in GPS at same time

On a trip I'll add:
12v air pump
J-box
Igniter

Don't forget that extra key somewhere!

On a trip, don't forget the thin plastic 55 gallon trash/leaf bag.  Great for keeping clean while kneeling or laying on the ground.  You can wear it in the rain or cover your duffel bag.  Use it to keep your seat dry and free of bird poop.  Keep the instrument cluster and switch clusters dry when parked.  Use it to put a tire on the rim with no tools.  Takes up zero room.  Perfect for collecting important pieces from the bike after a mishap.  I'm sure there are other things, too.......

Always bring a  spare throttle cable

On the bike, all the time.

Throttle pull cable, in place.
J-box
All bulbs
Shift linkage

Add on a trip:

Petcock
Front wheel bearings.
Speedo cable.

At home add brake pads, rear wheel bearings, tires, throttle push cable, alternator, K-trac, rear shock, coils and wires, ignitor, well gaskets, valve adjuster screws and nuts, air filter, oil filters, crush washers, grip heater, clutch star spring kit and nut, spark plug, cruise control(complete kit plus an extra servo), assorted Murphs' screws, rear TS assembly, saddle bag for parts, and more flotsam.

"Throttle pull cable, in place."

That's a great idea!

Always carry a spare O-Ring for the thermostat housing, this O-Ring will go and it won't give you much of a warning. The O-Ring will deteriorate and it will blow out and leave you on the side of the road. If your bike is over 5 years old replace this O-Ring the next time you do your valves.