A mobile bag filling system for filling bags with fluent matter, such as sand, and comprises a hopper, a flume, and first and second conveyor systems. The hopper receives the fluent matter from a source and an auger within the hopper moves the fluent matter onto the first conveyor system and transfers the fluent matter from the hopper up a ramping section to the flume. The flume directs the fluent matter into at least one holding receptacle, or sandbag. The second conveyor system receives the sandbag after it has received the fluent matter and moves the sandbag sufficiently to one side of the flumes to allow a user to fill another sandbag. The mobile bag filling system may also include a sandbag docking station configured to receive the sandbag after the sandbag has received the fluent matter and disconnected from the flume. The sandbag docking station and the second conveyor system are positioned such that when the sandbag is pushed toward the second conveyor system, the sandbag falls onto the second conveyor system. A string clamp automatically seals the sandbags.