Its all about the wattage (and hence the current /Amps ) each item draws.
Stock Alternator is rated at 14volts/20.8Amps at 5k revs which according to physics gives ~291Watts of power to use to run the bike. Note Alternators (from memory) usually have a fairly flat o/p rating over thier operation range once above a certain revolution (figure on 2k revs as safe bottom end?-made up guess but its for starters )

So if you bike requires 5amps just to run ignition Fuel injection (about 70watts -guess for starters)
then the break down could be as follows
Headlight -stock 55watts
rear lamp 5 watts
side lamps think these are 3.5watts each so 7watts
Fogs ? 55watts? x 2 110 watts
Heated grips I've seen quotes from 30Watts a pair to 28Watts each grip so you'll have to google the spec of the ones you have. assumed 35Watts total

so adding that all up we have ~282Watts of power drain.
Leaving ~10Watts spare for other sundry items of current drain, ie indicators,brake lamp (21watts!) dash lamps (left them out).
Not a lot of extra left when you consider it especially if its all on at idle when alternator o/p is lower.
Which is why I mention careful management of accessories is required (especially heated clothing spot light combos) as it wont take much extra load to start hitting the battery .
Note All the above is a quick fag packet estimate using expected values, if someone wants to research say the engine drain figures for a more accurate estimate please go ahead.