The first activity we tried was an assortment of padlocks of varying sizes.
This uses not only a pinch grip to hold the key but also twisting motion to turn it. I think that I saw a similar idea on No Time For Flashcards pre-blog days but I may be wrong. B didn't like this at first which surprised me. On the second outing he liked it a lot and tried to make them into a chain.
The second activity was some carabiners which B was able to clip and unclip together. Since they are three different colours we may use these for patterning at some point but for now B, R and A were all happy to make them into chains and snakes and necklaces etc.
So there we have it sometimes the unlikeliest places can turn up activities for you if you keep an open mind.