You will need: two see-through cups, water, salt. Some food colouring. Pipette or medicine syringe. Some beads. Raisins, Anything else you fancy trying to float or sink.
Pour an equal amount of warm water into the cups. Into one of the cups, mix salt - as much salt as you can dissolve. Now for the fun! Using a pipette or syringe, pour a tiny amount of food colouring into both the cups. What happens? The salt means that some things float!
Now try with other household items - beads, a cork, food.... see what sinks and what floats?