You can get stuff from charity shops or cheap household goods shops. Anything shiny or with an interesting texture works well.
I just grab anything from around the house that I think will interest ds and make a pile of stuff in front of him. wooden spoons, lemon juicers, old biscuit/tea tins, loofahs, egg boxes, sieves, plastic bottles with water or rice in and sheets of foil all work well.
Not all of mine are non plastic but they all went down a treat.
Nail brush Paint brush Mirror Magnifying glass Shells Big bell on a ribbon Little bells in an organza bag Lots of metal bracelets on a necklace Some chunky bracelets in metal plastic wood and woven string Scraps of leather Corks Wooden spoons Mini whisks
Do you have a drawer of random bits you could raid for spare buttons, old keys, broken jewellery etc. Or the kitchen for lentils, pasta shapes or rice, (perhaps dyed in a mixture of colours), scrunched up or hole-punched bits of foil. You can get interesting effects by combining two liquids/gels that won't mix e.g.vegetable oil, or syrup with coloured water.