If you’re going to use the chain whip you just made, you’ll also need a way to get that cassette off. A lockring remover is a must-have; unless you use one of the shady removal methods I’ve seen on the internet—which I wouldn’t necessarily recommend unless you don’t care much about the condition of the wheel after you use them. I recommend Park Tool’s iterations here that cost about $6, but you’ll need to buy the specific one for your brand/type of cassette. (By the way, I’m assuming you already have an adjustable wrench laying around somewhere to use with this tool. If you don’t, well, you’ll need one of those too.)
Every person who considers themselves a cycling enthusiast should know how to do at least some basic bike repairs. This is not just to satisfy an unwritten standard of being a bikehead, but because it has a lot of practical implications as well. It can make the difference between dealing with a minor issue quickly on your own or waiting a couple of days for a busy mechanic to squeeze you in. Moreover, in the long run, doing the dirty work yourself will save you a lot of money.