Use ribbons to create flowers and other things.
Use funnels and plastic tubes to make a water system.
Use tins and boxes to create a cool drum set.
Convert that bathtub into a ship.
Use icecream sticks to make a fence
Kids basically like toys that involve and engage their imagination. Once you start looking at mundane things around the house as toys for them to play, you will find that they will join in enthusiastically. Of course, it goes without saying that such do-it- yourself ideas can be age and gender specific. Like little girls would love to play model and pose. There are many delightful handmade jewelry ideas to try that any girl would love.
With boys, you have to think automobiles and mechanical kind of stuff that requires them to use their hands and their mind. They love the idea of bikes, cars, hunting and other building kind of stuff. This may seem like a stereotype, but it is also true to a large extent. What is more even girls may like to do war, bike and other stuff if they are tomboys and artistic boys would love to do some home décor and other stuff. There is no hard and fast rule and you can pick the ideas that works best with your kid/kids.