I always take a backpack to carry water, snacks, camera, sunblock, etc. It isn't anything special - just a relatively cheap one that I got at a local sporting goods store. If you are doing more than a day hike I would imagine you're need something larger and sturdier than what I have.
I also have a backpack that is not fancy. I bought this bag on a local shop and it doesn't even have a name. I have used this for almost 5 years now and it is still in good condition although the colors are a bit fading. I put all my stuffs inside it whenever I do outdoor activities.
I always carry water with me anywhere I go, and it is always a necessity when you hike, as well as some other basic stuff that you need to put in a backpack like mosquito repellent, sunblock, towel, meds, etc.
I'm a LL Bean fan, only because they are lifetime guaranteed. I always carry a small backpack with me when I go hiking. I have water and a snack in it. I also carry aspirin, bandages, sunscreen and things like that.