This spreadsheet (MS Excel, 10K) is a rough cut at estimating the amount of current available for accessories.
A few notes:
The actual capacity of the alternator is in question. The 742W figure in the spreadsheet came from page 19-3 of the 2003/2004 service manual and is also on page 175 of the 2003 OwnersManual. The 2004 manual and a lot of Honda's press material claims 660W. The 2003/2004 PartsCatalog shows the alternator as part number 31100-MCS-003, as does the current parts fiche. Honda may have determined that the 742 figure was unrealistic and backed off it.
The spreadsheet bases its figures on the alternator's full capacity, which is roughly linear with rotation speed. If you typically run at 4,000 RPM, use 80% of the capacity figure.
Many of the load figures are estimated, hopefully overestimated.
Lamps with multiple filaments are calculated using the highest wattage.
The load of things that get used intermittently (horn, windshield motor, headlight adjuster, etc.) are not included.
Whether or not sufficient headroom should be left for the ABS modulators is an issue of some contention. When in use, they are believed to draw a combined 40A (480W). Actuating the ABS would exceed the spreadsheet's calculated 21A of excess capacity under normal running load, so it is quite possible that the system was designed to draw current from the battery. It is unlikely that the alternator's full capacity would be available during emergency braking, as the rider would likely be off the throttle and the engine would be turning at less than 5,000 RPM.