just to clarify, mike's math with 180 watts is for the 15 amp alternator/dynamo. i agree, that isn't much to work with. if you have the 40 amp alternator, you have 480 watts to distribute. that can do considerably more.
with regular, 50 watt halogens, you can run your two front (pretty useless) factory headlights, two more front facing ROPS work lights, a rear facing rops, a seat heater and a small heater blower and still charge the battery.
also, don't forget, you can draw more from the battery than you put in for intermittant loads without it losing all it's power. as long as you charge it back up once your done. things like flashers and turn signals are off half the time they are "on" so their average wattage is half of their rated use.
i would think one of the most important things you could do when adding any loads to the factory system is run the correct size conductors with proper fuses and a good distrubution block.
12 volt systems are not very forgiving of poor connections so use good quality wiring, hardware and cover the connection points with dielectric grease.
amp