Most plastic bottles can be recycled, but most plastic bottle tops can't. Here is an orange juice top reused as a slug trap (with beer).
The handle on our lawn mower broke (bent) around the time the wood handle broke off a cultivator, so Scott attached the broken handle of the cultivator to the lawn mower handle and it's now good and stiff as new. Kept us from having to buy a new lawn mower handle and throw out the cultivator handle.
This isn't garden related, but rubber wine corks can be reused for a wreath commemorating a special occasion:
My mother-in-law made this one for me with rubber corks from our wedding, and had wedding guests sign them. Is that cute or what?!
How do you creatively reuse things that can't be recycled?