I am very sneaky, sir.But in seriousness: Once you've got a full-time job and have taken a good long look at your student loans, or the lien on a car, etc. $20 doesn't look like so much by comparison. (On the flip side, if you are eating ramen most of the time--and not by choice--then perhaps every little bit counts, but hopefully nobody with time to post here is in such dire straits.)
Even a
minimum wage job is around $7.15/hr. Three hours and you can buy a $20 game you might be able to comfortably play for 30-300 hours. And it'll be something you can put on your resume later, as well as a recurring source of income if you continue. If you have no particular skills or ideas, you can always try a bit of under-the-table yardwork for neighbors. It's not fun, but it's also something that's easy to do one-off.
So for all the 13 to 18-year-olds... Well, you've already decided you are old enough to see someone get utterly disemboweled with a chainsaw, so get a job! Honestly, you'll be quite surprised at first by how much spending money you suddenly have, and if you try for internships etc. you can get a jump-start on whatever you want to do after you finish schooling.