The list is going to be mostly USA specific ~~(I'll come back with links)~~, but many of the fittings are from Kegland (Australia), so we get a blend of "freedom" units and metric

We'll start with level 1:

Tools: Depending on what exactly your goals are, you'll need

• a tubing cutter
• a faucet wrench
• a crescent wrench (for attaching the regulator nut. 1^1/8^in nuts on the regulators in my possession)
• a cheap water pressure gauge (you can check on your hose bib outside).

I'll be specifying push-in fittings because they're so much nicer to use.

Kegerator: obviously not a hard requirement. You can build a "keezer" out of a chest freezer, or bore a hole in your fridge for the faucet, or even use a picnic tap on a keg in the fridge (but you'll also have to get your gas line in the fridge which means also putting the tank in there, or boring a hole for the line anyway)

CO2 tank: These come in 5, 10, and 20lb sizes commonly available at welding shops, and are almost universally swapped out instead of refilled (so don't get attached). Check your prices for a new tank on the internet before you go to the welding shop to buy one. They will likely overcharge you for the first tank (by a hundred dollars), but they'll like it if you bring them a shiny new one and might give you a discount. My 10lb tank lasts us about 6 months and I have a backup 5lb tank.

CO2 regulator: If you're planning on beer taps too, go for a dual regulator right away and save yourself the hassle (serving beer is low pressure vs high pressure for water). Try to find one with a threaded output ("flare") instead of a barbed output (or bonus points for having a push-in fitting already).

Keg: I use 2.5 or 5 gallon ball-lock cornelius (corny/soda) kegs

Gas and beer/water tubing: I use evabarrier only. All the fittings will be 8mm push-in (typically "duotight") so get a length of 8mm x 4mm for liquid, and 8mm x 5mm for gas. These are the conventions for beer, and I just followed them for water.

Fittings:

• 1x of the 1/4" x 8mm push-in fittings for the CO2 regulator
• 1x Gas ball lock (typically gray), 1x Liquid Ball lock (typically black). I'd go for a "flow control" liquid ball-lock fitting. They are just enough different to be incompatible, so make sure to get 1 of each.
• 1x 8mm x 6.5mm push-in reducer (for the tap faucet shank)
• 1 6.5mm (3/16") compatible faucet shank
• 1 beer faucet
• 1 novelty tap handle
• I always recommend a check valve on the CO2 line, but it isn't a hard requirement (until we plumb the water line in level 2).
• Optional: keg lid with diffusion stone (or buy the stone and attach it to your gas post to save a little, but you'll need matching hose and clamps.

Level 2: This assumes you have completed level 1 Additional tools: none!

I'm going to assume you have a standard angle stop (like your toilet) for your water line. And I'm going to assume your plumber was nice enough to attach a 3/8" (9.5mm) push-in fitting.

Tubing:

• 9.5mm evabarrier to connect to the output that we'll step down to our "standard" beer dispensing 8mm. I have about 4 inches of it before reducing

Fittings:

• 1x 9.5mm to 8mm push-in reducer
• 2x 8mm check valves for your gas and water lines (don't be backing up the system on either side!)
• 1x [liquid ball lock ](Liquid Ball lock)
• 1x inline push-in regulator if you don't know your water pressure and/or need to reduce it
• 1x continuous carbonator keg lid (you can move your diffusion stone to this cap)

I replied to a different comment with the list!