Definitely reading and writing.
Hopefully the book is there and being processed. Sometimes the delivery of the book to a person is delayed by the jail processing system from a few days to a week. Also, paperbacks only.
Is there a language he wants to learn? I sent one of those books and Sudoku books.
It took a long time for my family member to access the phone (three weeks), video visits (four weeks), and commissary (six weeks, maybe eight?), but that worked out after awhile.
I wrote letters about once a week.
I wrote a letter with instructions how to use the phone with our phone numbers.
Then one of how to use the computer (which I learned from someone at the jail by going there).
After the APs kicked in, family member figured most everything out and was moved to medical dorm where there was a tv. Still read and wrote lots.
I also went to local parks and other places where I bought post cards about our town and area and sent those frequently (2 -3 times a week) with brief notes. I think it’s just nice to receive mail.