There's a myriad of things you can add to, insert, clip on to bicycle spokes.
Here are some suggestions.
Pipe cleaners are brilliant, really quick, really effective and really easy. They can be a bit pricey but you don't have to use a lot of them to create fun effects.
Join them up to make spirals, circles, squares, off centre optical illusions, random wiggly worms and to draw outline figures such as flowers, animals... You can make fun 3D figures like spiders and stand up men that bounce under the forks, it's important to extend his leg into a spiral around the spoke.Combining pipecelaners with drinking straws or bits of straws is fun and makes the straws more interesting.
Which leads us to our next topic:
If you are using straws, use colourful drinking straws. You can cut them in little pieces and slit them open on the side. Paper craft straws will unravel if you try and do this.
You can cut a slit in the straw and wrap it around individual spokes. To create an impressive wheel by working with straws alone can be a bit more time consuming, as there is a lot of cutting incolved. It will need some patience to do something good. Choose bright colours and try combining them with pipe cleaners, bits of wire, buttons...
Spokey Dokeys: Coloured plastic balls that you fitted to the spokes of your bike so that when you rode around slowly they would clatter up and down noisily ... You can make your own with buttons and wire, self hardening clay, safety pins, badges, paper clips, pegs dipped in glitter, check out girls hair accesories and beauty stuff.
If you can't make all these things go up and down your spokes, don't worry they'll still look great!
you can just tie to your spokes or slot in them.
With a piece of string or a cable tie you can attach pretty much any small object to a spoke, as long as you make sure it is firmly attached and secure, you don't want them to fall off and get caught up in your wheel.Little cuddly toys, small cheap plastic toys for example halloween spiders...
You can slot postcards, playing cards, photos, pictures you've drawn on cardboard in between the spokes. Have a look at this link and read more about Spoke Cards
You can do the same with old cd's. They create great effects, going round and round, catching the light. Because they are heavier and more rigid it is better to secure them with tape.
Stuffing the Wheel
Looking at a bicycle wheel you will find that there is quite a bit of space inbetween the left and the right side of it. You can stuff this space with things like scrunched up newspaper or foil, tiny little water bomb balloons, don't blow them up too much, just enough so they form a nice round little ball.
It is quick and easy to cover a whole wheel with cardboard
This can then be painted on, drawn on, collageg on and even have a furry carpet on.
See the cardboard plate post