If you find yourself heading out for an all-day ride with the pockets of your jersey weighed down to your hips and your saddle pack barely closing, it's probably time to invest in a bigger bag. Preferably something like PRO's Maxi Plus Saddle Bag, which features an expandable compartment that allows you to adjust the size of the bag if you need more space to hold your burgeoning collection of essentials. It comes with two slim external side pockets for energy gels or small items, and it attaches to your saddle and seatpost securely via two hook-and-loop straps. PRO made the accenting along the bag reflective, so it'll help increase your visibility during long rides that leave you out on the roads until sunset.
Prevents cycling essentials from cluttering your jersey
Expandable compartment accommodates a spare tube and pump
Two slim side pockets are ideal for stashing extra energy gels
Attaches to saddle via two hook-and-loop straps
Nice roomy bag
Familiarity: I've put it through the wringer
I like this bag for long rides in remote areas where I need to carry a couple spare tubes, tire levers, air canisters, multi-tool and more. I thought it would be embarrassingly big/unsightly on an aero bike but it is not (to me). A little more resistance than I would like around two of the corners when zipping open/close (whether bag is full or not). Fits nicely under my Fizik saddle. I would buy it again.