What to do with “dead time”?

For people currently in the workforce or people still doing their undergrad/masters, what did you do with your "dead time" in order to become more qualified outside of your undergrad? I'm talking getting certified in SQL, Python, etc., that sort of stuff. I used to major in biology but switched after I realized how narrow my career prospects will be if I go down that patj so I switched to Economics in hopes of eventually being able to do something in the broader conservation/sustanability field but I'll be happy with anything. Most of my friends from my biology days are either pursuing a masters/PhD to kill time because they can't find work and the prospect of more academia makes me queasy. I feel so underqualified 🙁 I feel like I know less than I should at this current point in time and that everyone already got a head start in econ. What can I do to become a more desirable candidate?