A good multi tool has nearly everything you need, but there are a few separate tools every cyclist should have. Either they are too big for a multitool, or they just make life easier.
First, every semi-serious rider should have the tools required to remove a cassette. You definitely need a chain whip like a Park HCW-16, and you definitely need the cassette lockring tool, like a Park FR-5. The chain whip is about $25. The reason I wish I had the HCW-9 is because it also has a 15mm pedal wrench built into the back side. Two tools for the price of one, basically. The cassette lockring tools are about $10 or less. I already had a big adjustable wrench to fit the lockring tool, so there was no extra expense there. Park and other companies sell long wrenches to fit the lockring tool, but an adjustable wrench is totally fine. That’s $35 well spent. Now you can switch your gearing to match the route you are riding, you can take your cassette apart and clean it, or you can swap your cassette from one set of wheels to another.
Next is a set of metric ball end hex wrenches. I got mine from Steve’s Tools for under $10. Harbor Freight has basically the same ones for under $10 too. Make sure it goes down as small as a #2 (2mm) and up to 10mm. That will give you a small enough wrench to remove your brake pad cartridges, and large enough to remove cranks. The ball end is really great for hard-to-reach bolts. For example, the bolts to mount your sram shifters to your bars. It’s really difficult to get a multi tool at the right angle to get to these bolts. Same thing with bottle cages. Some cages are easier than others. An L-shaped hex wrench with a ball end will give you leverage to loosen the bolt, and the you can switch to the ball end to quickly unscrew them without having to constantly take your wrench off the bolt, rotate it, and figure out where it fits again. $10 well spent.
Next is a Park CC-2 Chain Checker. Actually, a CC-3.2 is a way better purchase at 1/3 of the cost of the CC-2, but the CC-2 looks cooler, which is how I got suckered into buying it. The nice thing with the CC-2 is that you can see when your chain is .25, .5, .75, 1.0 or anything in between. The CC-3.2 is just a “go/no go” kind of tool. Chain replacement is really important. A worn chain will quickly wear your cassette and chainrings. Plus, it won’t shift as well. Waiting too long to replace your chain will cost you a lot more money since you will have to change out more stuff. Changing the chain out too soon is also a waste of money since your not getting all the miles you can out of a chain. You can also use a ruler to measure the chain, but a chain checker is easier. You can get a decent idea of how stretched your chain is by shifting into your 53/11 (or biggest gear) and grab the chain at 3 o’clock as you’re looking at your crankset. Pull the chain towards 3 o’clock and if the chain lifts, your chain is starting to stretch. Depending on how much of a chainring tooth you see, it might be time to swap chains. It’s a really rough measurement, so you are way better off with a real chain checker or ruler.
Last, the Bontrager Preset Torque Wrench. Did you know that too much torque on your seat post clamp or stem bolts could cause a lot of damage to your bike (and face)? With most carbon steerer tubes, handbars, and seat posts, the manufacturer recommends using 5Nm of torque. “Real” torque wrenches are pricey. For $20, you can get Bontrager’s preset torque wrench with a 4mm hex key. The 4mm fits most stem bolts and seatpost clamps, but not all. It’s a nice tool to have at a race. You never know when a crash is going to knock your saddle or bars out of adjustment, and you want to make sure you can properly torque the bolts after you readjust them. On a side note, this is also a great tool for speed skaters. I usually tighten my wheel axels with it before I race, since they are also 4mm.