The Czechs know how to make cheap but durable surplus. 

These shoulder bags are rubberized so they will keep your goodies inside dry. 
They have a thin but adjustable shoulder strap and two friction buckles to help keep the bag closed. Inside the bag has a divider which is split into two compartments so you can keep your goods separated. 

And with a little bit of work and extra straps, these make great saddle bags for your bike. 
 
The bags measure approximately 9.5" x 4.5" x 9". 
 
Since these are used surplus bags, please expect fading, small tears, stains, fraying, and/or markings.