Can you take the bladder out of this pack...
Can you take the bladder out of this pack and use it in a daypack?
Yes, especially if the daypack in question was designed for or came with a hydration system as most are these days. I would highly recommend Camelbak, great burst proof bladders (nothing worse than a wet back on a winter day), and tons of accessories for customizing it to your application. Easy to clean too!