I cheated and first of all bought a ready-made art tub from John Lewis, containing things like scissors and glue and pipecleaners, as well as glitter and buttons and such like. I realise he is still a little young for this sort of thing, so also bought some plain coloured card and finger paints ("washable", they claimed).
To prepare the kitchen for paintageddon, I dug out my huge Cath Kidston oiled tablecloth (which no longer serves as an actual tablecloth), and stripped the boy down to his vest. What's the worse that could happen?
Turns out, 17 month old boys can be surprisingly creative with paints... Just not really in a way involving say paper, or painting.
Then there are all the other surprising uses for paints: eat the paint, touch the paint, throw the paint (Pollock-esque?), cover hand in paint and then run madly towards the soft furnishings... Pretty much do everything with paint other than paint the paint.
But with fast reactions and quick timing it turns out you can slide that bit of card under whatever mayhem is going on, in order to catch some artwork as a byproduct. Result!!