Murphy's Law states that if you go for a bike ride without your tools you will need them. Bring your tools!
From Park Tool:
The Park Tool Fold Up Hex Wrench Set combines all the popular hex wrench sizes into one convenient fold-up tool, eliminating the need for a mess of loose tools. Its multi-position composite handle is comfortable, lightweight, slip-resistant, and 40% stronger than steel handles.
Includes 4mm, 5mm, and 6mm hex wrenches and Phillips and flat blade screwdrivers
Wrenches made from industrial tool steel, through hardened and tempered for long life