On a Windows PC, learn the “charmap” application (charmap.exe). You can run it from Start / Run / charmap. This will show you ALL of the characters you can type on nearly any keyboard (including characters in languages you may never have heard of). You can find the characters you need, “select” and “copy” them for pasting into other applications or documents.
If you look around, you can also learn how to enter a lot of common characters, such as °, ÷, ¥, £, ¢ and others (anything you want, really, if it’s an ASCII character) using the Alt key and the number keys from the numeric keypad. I think what you’d want to look for is “ASCII” in Wikipedia. That’ll get you a good start.
There are also easy programs to enable you to “remap” keys on your keyboard into characters that you frequently require.
You can also use Microsoft Office programs (and others, I suppose, but I use Office) to do “Autocorrect”. So, for example, I can set up an Autocorrect in Word or Excel that will look for times when I type in $yen$ and have that replaced (automatically, as I type) with ¥.