I was just going thru a closet and found my Moms card box. She always kept Christmas cards from year to year finally donating them. When she lived with me, I bought a box and put cards she received in them. A couple of Church ladies sent one every month. I left it where she would see it. She had a table she ate from. She would sit, read, and sort out the cards. Kept her busy and happy.
My dad with Alzheimer's always wants to "help", and I find sorting activities especially useful to keep him occupied. He was a mechanic, so we have a workshop full of screws, nails, washers, etc, that all need sorting! Over and over and over again! Coins, too. And buttons, by size, shape, color, etc.
Another good activity along the "helping" lines is folding towels and sheets. I have the aides pull all the towels out of the linen closet and dump them all on his bed, he loves to help fold them. For patients with severe short-term memory loss, you can repeat these activities as often as they help.