We have spent so much time outdoors and chalk and pots of water with brushes have been filling lots of time. We have a permanent outdoor chalk board and we have also had the easel up and of course the patio is popular. We used lots of different sizes and shapes of brushes and sponges and also some normal sized chalk and giant chalks.
I found this from the imagination tree inspiring too, which was all about putting chalk on the board first and letting the kids paint out the chalk with water which has also been a great activity that doesn't create too much mess!!!