My nephew-in-law was in the county jail and the restrictions were absolutely ridiculous. He could have paper, envelopes, and stamps but no writing implements, a picture no bigger than a 5x7, no newspapers or magazines, no personal items, no books--even something as simple as a crossword puzzle book. He could have a deck of cards. No cash, but money orders could be left to be put into his account for use at the commissary.
Your best bet would be to either call the jail where your uncle is located or find their website (look under that county's offices) to find out what the restrictions are.
I was also able to take tennis to my nephew-in-law because he was on a work detail. The item he treasured most was a pic of his kids that I took to him. Even then, I couldn't take it and hand it to him; there were specific drop off times that items could be taken to the jail, inspected by the officers, and if they passed inspection, then they were given to the prisoners.
I had no idea there were so many rules and regulations involved. Be sure to check first.