I want to add a single outlet at this box, which I'm assuming is just a junction box(?). What parts would I need to buy in order to install an outlet here?

[i][b]314.29 Boxes, Conduit Bodies, and Handhole Enclosures to Be Accessible. [/b][/i][i]Boxes, conduit bodies, and handhole enclosures shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or structure or, in underground circuits, without excavating sidewalks, paving, earth, or other substance that is to be used to establish the finished grade.[/i] I know nothing about electric, forgive me, but I've never seen/noticed a blank cover plate on a ceiling where new recessed lights have been retro fitted. I'm guessing people/contractors just tuck them into the ceiling and drywall patch over them. New recessed lighting was installed by an electrician in a few downstairs rooms. There's a second floor above this ceiling, not an attic where boxes can be accessed from and therefore be OK to just bring the box up a bit so it can be drywalled over after a blank plate is installed. I understand if the new wires are spliced into the old box (which originally only fed a ceiling light), then the box now may need to be accessed (but also, why would you even need to access this box even if a light goes bad, wouldn't it %99 of the time be the actual light/wiring in the light fixture and not a problem with where it splices into the junction box? Hence I think most people just bury the old junction box. Could a short circuit or something fry the wiring or something and thus need junction box access to repair? Or is it just for convenience if new lighting is installed again in like 20 years? (but again, they'd have to cut up the ceiling quite a bit anyway for that and it would be pretty easy to find the box then). I'm not sure if the new lights even connect to the old junction box, I can ask the electrician or maybe tell by if there's brand new wire nuts/wires/tape on the wires (house build 1980 and original parts will look older). If the new lights are NOT connected to this junction box, then is the only reason you shouldn't hide the box in the ceiling (after cover platting it at least) be simply because if someone has to cut a hole in the ceiling for whatever reason (drywall repair etc) then they wouldn't know the box is there and could hit it with a saw or something? But then, that goes for anything really - e.g. IMHO one shouldn't just assume studs are exactly 16 on center or no pipes etc even after checking with a stud/electrical finder, I don't recommend basically replacing baseboard moulding and just going shooting all new nails everywhere - you should gently cut and check/confirm sides of studs and no wires/pipes/ducts next to them or wires not ran through drilled-out studs where the electrician might have skipped the safety stud wire metal plate that would bend a trim nail or stop a screw from entering. And then sloppy quick patch (to meet fire code) the hole and baseboard will hide it anyway, or if on a wall for shelves etc may have to patch and match previous paint but better than hitting a wire/pipe. - If the box isn't even needed anymore (doesn't tie into new recessed lights) then why not just cut the nails holding it to the joist, cover plate it and then push it up into the bay and install a wood block + metal safety plate underneath it so that if someone does go cutting open the ceiling to repair drywall or something they would hit that and stop instead of the wires (again, though there's wires/pipes etc everywhere in walls anyway). The old junction box probably IS being used though, right? But still, tempting to tuck up and safety plate and block it from being cut by accident, because again, I've never seen what is supposed to be done which is to use a blank cover plate and paint it the same color as ceiling that's about to be painted. I guess the old junction box IS probably connected to something that still needs power (another light in another room or outlet etc) and can't just disconnect it from the breaker box, and it probably IS connected to the new recessed lights, but still wondering what people do about this since I've never seen blank cover plates used and it does look tacky.