clean paint brush and bucket full of water for him to 'paint the house/deck/car/whatever'
empty egg carton, spoons, scoops, a bowl of rice, a cup of water and some shakers with spices
a clean cookie sheet or two, shaving cream to smear all over the sheet, and child buckled into chair
how about usually 'off limits' stuff- office supplies always intrigued Nick- envelopes, his own scotch tape, hole punch.
very shallow kiddie pool with boats/vehicles- barely water in there with your eyes on him- shaving cream in tub on walls too for finger painting.