All kidding aside, here's what I would call a basic list of must-haves for anyone starting out in this hobby.
1. Refractometer (or calibrated swing-arm hydrometer)
2. 5g buckets. You'll need at least 2 or 3. The easiest way to get them is to buy your salt in them.
3. 2 heaters rated to ~3/4 your tanks size. 2 smaller ones are better than one larger because heaters fail. Usually in the "On" position. I keep a couple spares on hand as well.
4. Nets. At least 2. As someone who worked at a LFS for about 10 years, trust me on this. It is WAY easier to catch a fish using one net to herd the fish into the other than it is to chase a fish endlessly with just one.
5. A 10 or 20g tank to use as a QT. You can pick one up at Petco for $1/g. A basic freshwater "starter" kit will suffice - it will have some sort of filter and heater that will do the job. PLEASE do not skip QT on ALL new fish. You only need to wipe out one tank full of fish to understand the idiocy of not using a proper QT!
6. Test kits, as mentioned above. API works well for initial cycling. I prefer Salifert for Calcium, Alkalinity, and Magnesium due to their ease of use and repeatability.
7. Water change equipment. You can use a piece of vinyl tubing and a couple of those buckets (see #2), or better yet, invest in a Python Siphon and you don't have to worry about over filling a bucket with nasty water and then spilling in on your wife's carpet. (another lesson learned the hard way, tyvm)
8. RO/DI system. Invest in your own. It will quickly pay for itself.
9. Water storage/mixing container. The largest you have room for. I've been at this for about 30 years and I have yet to run into a situation where I thought I had too much water on hand. I have, however, run short on too many occasions. If possible, I would suggest having enough ro/di water on hand to handle at least 75% of your systems volume. I keep mine heated at all times, and have a old power head in it to mix salt for me.
10. Activated carbon. You can run it in a reactor or just toss a mesh bag in the sump. You don't have to use it all the time although many do (myself included). It's very useful for removing toxins from the water.
11. Polyfilter - used for heavy metal contamination.
12. Patience!!! NOTHING GOOD HAPPENS FAST IN THIS HOBBY!!! Don't jump straight to Panic Mode if something doesn't look right. figure out what the problem is, then take corrective action.
13. When asking for help - COMPLETE Information please! Tank size, age, lighting, parameters (actual numbers for all - not "their all good"), pictures of the problem speak volumes.
I'm sure there is more, but that's a good start.
Oh - and don't forget $$$$$$$$$$$$$$$$$$$