Sample suggestions for phase contrast microscopy
Any green, soft leaf from a non-toxic plant is a good start. Cut a thin slice from the leaf (either to look at the cross-section or the surface). Try different leafs with different colors - there might be colors in the cytosol and/or in chromoplasts.

Concrete example for dynamic structures:


Elodea leafs: they consist of only two cell layers and can be looked at under the microscope without further preparation. Keep the the leaf in water and cover it with a cover slide before looking at it under the microscope and add water when it starts drying out. The green chloroplasts in the plant cells are moving around as long as the cell lives.


You might find Elodea either in a pond or in a store selling aquarium fish and the like. You can keep Elodea alive and grow it in nutritious water at a sunny place.