Some possible methods to help plastic single use straws stay useful. 

Glue some pretty colored ones around a interestingly shaped jar (plastic) to cover its and enhance the pens or flowers  you put in it.  One could continue gluing and snipping straws into the flowers. I am thinking back to my 4-H days and the basketry project, weaving bendy materials around stiff ones.  Learning to lash a stiff framework together to support the final larger project. 

The Fairy /Gnome / Toad home for your mantle, bookshelf, table centerpiece, garden accent, place mats whatever your cleverness imagines.  My many catalogs offer overwintering shelters for insects.  Mine was of bamboo  and lasted most of a year. I am sure I can cobble together a sturdier one using straws.  As for mosaic and collage there are many options.  Realistic, abstract, protest piece with message, funny pieces,and 3 D are all possible.

Flattened straws, distressed straws, short straws, long straws, bent straws. Straws you leave in your parking space to be run over and over. Straws you let the neighbor kids smash with a stick. If you want to be a purest and use found abused straws start now! Fast food areas are well groomed.  Maybe if you get there early...or...late (between shifts).