Don't tempt fate.
The day you don't bring your pack is the day an hour-long cruise turns into an all-day epic, so you don't want to risk leaving the Shimano Rokko Bike Hydration Pack at home. Calling the Rokko a hydration pack is selling it a little short, though, because while it does comfortably hold a reservoir and secure the hose to the shoulder strap, the main compartment is also big enough to hold a wind shell, food, and sunscreen. Shimano also integrated two side pockets for bottles, a fleece-lined pocket for your phone, and an internal pouch to keep tools, tubes, and patches organized and easy to reach.
The Rokko isn't all about what you can fit into it, though. A helmet carrier and sunglasses clip let you stash extra gear on the outside of the pack, and the stowaway raincover pulls out of the bottom stash to keep all your gear dry when dry and dusty singletrack is transformed into a muddy river. If your day's ride is an urban commute instead of a trail ride, the Rokko's light clip and reflective details light up the night, to help ensure you don't get run off the road by inattentive motorists.