Motorcycling is a great way to guarantee you'll spend little to no money on things you don't need. Aside from the obvious expenses, you'll find ways to spend money on accessories instead. It almost can't be helped. Accessories offer you a way to elevate your experience, and can also be extremely useful.
Yeah, we're starting with a very general one, but it's one that is always worth repeating. Buying all of the correct riding gear (helmet, jacket, gloves, pants, boots, etc.) is one of the most essential things you can do as a motorcyclist. You can't skimp on it. If you don't pay for the right stuff, you could end up paying for the wrong stuff.
Another general set of accessories is basically its own category. Seriously, this is one deep rabbit hole…but one that pays for itself. As you become more and more of a mechanic, you get more and more in touch with what makes your motorcycle tick, you save money as you become more familiar with certain repairs and service procedures, and you add to your satisfaction. It's a win-win-win…win.
A set of motorcycle luggage can be incredibly useful. Whether you are going touring, moving a few things from point A to point B, or going shopping, motorcycle luggage has you covered. Saddlebags are the quintessential motorcycle luggage items, but you need not stop there. You can increase your capacity by supplementing them with a tail bag. Throw on a tank bag, and you're ready for anything. You can opt for soft luggage or hard luggage, depending on your preference and/or purposes.
This almost seems like a no-brainer, especially for those of us who live in colder climates. You can get heated clothing that runs off of your motorcycle's electrical system, or that is equipped with its own power supply. While not necessarily cheap, heated clothing is a great way to ensure comfort and to extend your riding season. Simple enough.
Light-emitting diodes have a number of advantages over filament bulbs: they are more efficient; they are smaller; they don't burn out suddenly; they have a much longer average life span. These factors really make sense when it comes to use on a motorcycle. As well as being great functional modifications, they make for stylistic modifications as well.
Nobody likes to think about crashing, but with crash protection such as frame sliders, bar ends, swing arm spools, and fork sliders, you can minimize your worry. For just a few bucks, you can protect your motorcycle from damage resulting from moderate to low-speed slides or tip-overs. Replacing crash protection is cheaper than replacing plastic and hard parts.
Not everyone is fortunate to have a garage, but that's okay because covers are a decent option. They offer protection from the elements, lazy goons looking for a random seat, and prying eyes. Sure, anyone can cut right through one, but that takes time, and you will probably also have a security system (see below) to help out. Think of motorcycle covers as a deterrent that will turn away all but the jerkiest of jerks.
Motorcycle security systems range from a variety of locks to sophisticated electronic alarms. GPS tracking can even be had these days. Having a motorcycle stolen is no fun at all, and any sort of security system can help keep it safe. Even if you're not in the immediate vicinity, an alarm will alert others, while locking systems will make stealing your bike difficult, or not worth the trouble for would-be thieves.
Visibility is your friend out there. Obviously, it drops dramatically after sundown, so some strategically placed reflection will help you out. You can get reflective license plate bolts, or you can use reflective tape on certain surfaces. Some riding gear comes with reflective tubing or panels, so consider those as alternatives.
There is a wealth of information for motorcyclists out there, so take advantage of it. A multitude of books have been written on riding technique, mechanical aspects of motorcycles, and even on health and medical issues pertinent to motorcyclists. Motorcycle books are a valuable resource in your quest to get the most out of your motorcycling life. Your best motorcycling accessory is your mind, so feed it.
Obviously, there are TONS of motorcycle accessories out there, ranging from the general to the specific. These are but a few suggestions.