It sounds like you're probably using an access token retrieved via the API Explorer though. The API Explorer has early access to an upcoming feature where an app can retrieve access tokens that are short-lived. If you use your own app to get an access token instead, e.g., via the OAuth flow, or just by clicking the "Generate" button on the app's info page on the App Console, that access token won't expire by itself, so you can store and re-use that long term instead.
We love to learn from the educators who use Dropbox. Whether you teach kids, teens, adults or a combination of all three, we want to know what apps and integrations you use with Dropbox to help with teaching. Which of the ones below is your favorite, or most used tool?