This table alphabetically lists the eight after-school activities available to teens, what skills they develop, and what days they meet.
A young adult who can quickly get to the mid levels of their career track will have more than paid for any money lost by not having a job. In the long-term, job skills are more important than money, as they'll lead to faster promotions. Note that signing up for after-school activities will hurt the teen's chances at holding a part-time job, but this is arguably a net positive. Also, you never have to sign up for two you can sign up for only one if you choose.
You aren't allowed to sign up for two activities that meet on the same day, but otherwise there are no restrictions. It can be tough to choose which ones to go for without a cheat sheet, but that's what the wiki is for! Look at the bottom of this page for a table with all the activities, the skills they advance, and what days they meet.