Here is a video of one of my favorite YouTube channels " Intense Angler" which shows different usage of drinking straw for hikers:
http://www.youtube.com/watch?v=WiB9kUPRXZ4
I carried a straw for a long time not knowing how versatile it is
I might add just two more to the list :
1- Drinking from small streams is much easier and cleaner with a straw
2- Blowing air to small fire especially a wood burning stove is easier with using a straw and you can avoid filling lightheaded using it.