If you've been doing some grouting with cement-based grout and have some left over, here are a couple of ideas. They're quick and easy, because at the end of a grouting session you don't especially want to start something else. These don't really work with ready mixed tile adhesive/grout - it's just too sticky to be workable.
This Fly Agaric toadstool was made from some grout formed into a small pattie about 10cm (4 inches) across on a piece of plastic. Pieces of thick mirror have been pushed right into the grout, so that they are flush with the surface. When the grout is set and dry (at least overnight - a day or two may be better) it can be carefully lifted off the plastic and painted with red acrylic paint. Clean any paint off the mirror with a cloth or tissue at once. The base can be any suitable cylindrical object made of, for example, ceramic or wood, stuck on with a very strong glue.
The cats, the rather manic rabbit
and the crab (below) were cast by pressing grout into jelly molds. If there's only enough grout left over to half fill a mold, that's fine, just top it up next time.
They need several days to set. To free them easily, smear some petroleum gel on the inside of the mold before casting, but generally they can be released just by flexing the plastic mold. The mini statues can then be painted with acrylic paint – a fun project for kids - and can go in the garden.