Some Civics came with rear discs (EX?)

You'd need the parking brake cables, proportioning valve, discs, backing
plates, mount brackets, calipers, new flex lines, etc., and maybe even the
trailing arms and wheel bearings

I would not advise the swap. You will get no better braking and a LOT more
maintenance issues. Stick with drums. They don't look as cool in between
the spokes of your $400 wheels, but they are better than discs in practice.

You won't see any better braking, only a "bling bling" factor.

You'll need master cylinder, prop. valve, ebrake cables, trailing arms
complete to hub assembly, and different brake lines.

Also figure on cutting out EACH bolt on the back.

In short, not worth the effort.

you need the right proportioning valve, hoses, backing plates/hub
assemblies, hand brake cables and of course, disks & calipers.  you also
need a t50 torx driver.  use a good quality one - NOT lisle.  lisle make
good tools for many applications, but their torx drivers are grossly
inferior.  i rounded off two before i finally figured out that it was
the tool, not the backing plate bolt.

a lot of people change out the whole trailing arm assemblies, but that's
not essential, particularly if your trailing arm bushes are in good
condition & the donor vehicle's aren't.  leaving your old trailing arms
in place also means you don't have to do a new rear end alignment.

if you're going to do this, you may as well go for the big disks on the
front as well, 10.25" vs 9.5" standard, and if you do that, you'll need
bigger calipers, the bigger diameter master cylinder & the bigger vacuum
booster.  the steering knuckles are not necessary unless you're worried
about the splash plate being slightly too small.  unless your climate is
absolutely abysmal, i really can't see it making any more difference
than having spoked alloy wheels vs steelies.

here's what i've worked out on proportioning valves.  if anyone else
knows different, please post.  there's a number stamped into the one of
the two main halves near where they're joined.  if your original
proportioning valve reads something like "3025" and you get rear disks
from a vehicle reading "4040" [like an integra] and you /don't/ change
the front disks, you need a "3040" proportioning valve [from an 88
accord ex/s].  if you do use the bigger front disks, you need the 4040.

master cylinders are best changed complete with the vacuum booster as
the bolt-on patterns are different depending on model/year.  just so
long as the brake lines align.  the closest fit for my 89 civic, without
doing any re-plumbing, is the 88 accord again.  it has a 15/16" piston
diameter.  i'd prefer a 1" cylinder from a del sol or an integra, but
that requires a different brake line fitting.  not impossible, but it's
not as close to being direct bolt-on as the rest of the conversion.

some day, i'll get around to sending "how-to" pics to tegger for hosting.