We know that Thursday night is pizza night and Saturday is a laundry day. What others activities (done by individuals or the whole group) occur on specific days?
Monday Night: Thai Takeout Night(this has all the activities posted by weekday)
Tuesday Night: Cheesecake Factory night.
Thursday Night: Every 3rd Thursday of each month is Anything Can Happen Thursday. The rest of them are Pizza Night.
Friday Night: Vintage Video Game night, also order Chinese Food night.
Saturday Night: Laundry Night of course.
Sunday: No "usual" activities.
There is also the anything-can-happen Thursday, though I'm not sure how long that went on for and when it was swapped for pizza night.
It might also possibly be mentioned at some point that they visit the Cheesecake Factory on Wednesdays, but I'm not entirely sure.
I don't think any of the other weekly day-specific activities are mentioned by which night of the week they are, but from the names of them we can assume that they occur weekly, such as:
- Vintage video games night
- Halo night (likely discontinued)
- New comic book night
There are probably more, but these are the only ones I can remember at the moment. If any more are revealed/remembered I'll edit them into my answer.