Depending on your subwoofer's current draw, you may need a capacitor to help power it especially if you plan to have your stereo playing while the engine is off. The other stuff are all low-current draw (1-2 amps at most) while the engine is running - this is more something your alternator has to deal with rather than the battery.
You can even just bring your battery into a store to have it load tested. If you really want to replace the battery for peace of mind, do it. But its not necessarily for those accessories you mentioned.
You can even just bring your battery into a store to have it load tested. If you really want to replace the battery for peace of mind, do it. But its not necessarily for those accessories you mentioned.