If your charging system is well maintained and up to snuff it will support a heated vest or a aux. light etc. If you want to run a couple of lights and a vest etc. all at the same time you would need a system upgrade. On my stock system I run a vest and a PIaa 35 watt light at the same time without issues. Though I am in the habit of shutting something off if I go through town and the revs aren't being kept up.
"Between two explanations, choose the clearest; between two forms,
the most elementary; between two expressions, the shortest."
Between two motorcycles the simplest (DW)
Eugeni d' Ors (1881-1954); Spanish writer.