BBB has all the best tools & accessories for your bike including on-board storage bags like the TopPack Top Tube Bag.
Designed specifically for mounting on the top frame tube it will keep the contents quite dry and dust-free under most circumstances.
Plenty Of Room Inside
This very handy little storage unit offers a sweet 720 cm3 of space to put to great use. The main compartment (with zipper closure) has room to stow things like energy bars/gels, wallets, keys, small cameras or mobile phones, etc which may be too heavy or bulky for a jersey pocket.
Transparent Route Map Section
A top flap doubles as a weather shield and a transparent cover for a route map or small document holder. There's also a hook & loop fastener keeping the flap secured while the bike is in motion. The bag has three (3) buckle/hook & loop straps locking it onto the bar and for added good measure the bag base has an anti-slip panel to keep it from drifting.