"Bolt ons" means anything you can run without getting into the internals of the engine pretty much. Exhaust parts, gears, intake tubes, pullies, that sort of thing.
Nowadays though with newer cars the factory does such a good job with all that stuff that all you need is a tune/gears/exhaust. A Coyote or even a Cyclone Mustang for example. Tune, exhaust, maybe gears depending on what you have and that's really it as far as power.
Suspension is often overlooked like a mofo too. Witness the dozens of Whipple'd GT500 owners that can't even run a 10 because they are on mostly stock suspension but oh man they have that 700rwhp dyno slip...
For a 2V the common "bolt ons" would be:
-Shifter or J-mod
Then do suspension. Lower the car, CC plates, lower control arms, nice set of wheels/tires, subframe connectors too are pretty much mandatory.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.