Batteries!

[m in sc]

led headlights and bulb lights go a long way as well. 

[Dvsrd]

I'd carry a cheap small LED torch or headlamp for any roadside problems or emergencies, instead of relying on the bike battery and headlights for that  purpose. In my opinion, the main argument for 5Ah or even more, is the parking lights. The taillight bulb draws 5W, and I guess the front is somewhere between 3 and 5 w. So stock parking lights woill draw close to 1A, giving 5 hours of light at best. Now I am not sure what's available, but LED bulbs would cut the current draw significantly, and a smaller battery would be absolutely fine, especially with a magneto CDI setup like Powerdynamo/VAPE/Banshee/HPI where the ignition is self generating. No battery is not that great IMHO.
   

[m in sc]

(all bulbs stock type)
an 1157 draws .83a on low @10w, 2.6a on high.  1156 is roughly the same on low.

headlight @35w is roughly 2.9a

figure .4a for each gauge bulb.

+ coils, and turn signal relay of stock. it adds up quick.