Brokerage login now requiring I answer these questions. Not a single one of these has a single answer I’d actually remember. They all have problems regarding what would actually count or multiple possible answers to choose from, or these are not things people would remember or they just don’t apply to most people.
One method to approach this is to use a simple personal algorithmically to create answers here. As in, you could put any security question in front of someone that uses this method, even those questions never seen, and the personal algorithm would produce an answer only the user would know. Here are a couple algorithms I made up to show an example for this post.
Input security question (the first from OP’s list): What was the first stock you ever bought?
This way you don’t necessarily have to write down your security question answers. Most certainly never write down your personal algorithm. Using this method it is trivially easy for you (and only you) to produce an answer from any security question given to you and equally easy for you to reproduce the answer when you need it in the future.