Make a collection of old costume jewelry, buttons, bottle caps, soda cans, pens that have run out of ink, or just about any material that is usually considered trash. Garage sales, basements, and stores offer plenty of material.
Once you have enough to play around with, have fun seeing how many different ways you can use something! Can you build with them, make a collage, or count and sort them?
If your kids ask what something is, help them figure it out themselves by asking leading questions and giving hints. How many odd things can your kids identify?