Water in a bucket: I use one of the flat buckets or a big tub (big and not too tall) I put some water in it and then I give him some toys and wash cloth and just let him do his own thing. They will find ways to amuse themselves with the stuff given But I always supervise him when hes playing with water and I always put towls on the floor, because sometimes he would pick up the tub and walk around with it and if it spills might be slippery. Sometimes I would put bubbles in the tub and he LOVES it. He loves putting wash cloth in it as if washing.
The flour in the tub: pretty much the same thing, I put a towl on the floor and put some flour into the tub then give him a spoon, spectular, wooden spoon, plastic cup and some cotton buds (for some reason he loces cotton buds), and I would hide the cotton buds in the flour and then he would sit there for hours digging into the flour with spoons, scoop them into the cup then out again, find the cotton buds then hide them again, sometimes he would just put the flour in his paml and squeeze it and finds it amusing~ I usually dont watch him when he plays with flour, but lot of cleaning afterwards lol.
Just another thought, my DS loves birds and thomas the tank engine, sometimes we would go through magazines together looking for the pictures then cut them out and stick them onto a book and he loves going through his book looking at them.
Also fridge magnets keeps them entertained too, I got him some action figure ones from some cheap shop and he would stand there for a long time sticking them on and taking them off while I do the dishes!