Quoted By:
I use a Geigerrig hydration pack (pic related) has room for 3l of water, and about 2 energy bars, a water filter, and some trail mix, with just enough room to stuff my rain shell in it.
I then keep a knife, FAK and a dump pouch on my belt. Sometimes my camera which has a belt holder as well.
Keeps me from bringing too much shit on a day hike, and gives me plenty of options.