How to set selected item in reactstrap Dropdown?

Similar to @Nevosis solution, you can add a value attribute and get it afterwards on the "onChange" event:

    onDropdownItem_Click = (sender) => {
    var icon = sender.currentTarget.querySelector("i");
    var newState = {
      dropDownValue: sender.currentTarget.getAttribute("dropdownvalue"),
      dropDownIcon: !!icon && icon.getAttribute("class")
    };

    this.setState(newState);
    if (!!this.props.onChange) {
      this.props.onChange(newState.dropDownValue);
    }    
}

  render = () => (
    <Dropdown isOpen={this.state.dropDownOpen} toggle={this.toggle} className={'ticket-module-selector ' + this.props.className}>
      <DropdownToggle color={this.props.color} caret>
        <i className={this.state.dropDownIcon}></i>{this.state.dropDownValue}
      </DropdownToggle>
      <DropdownMenu>
        <DropdownItem onClick={this.onDropdownItem_Click} dropDownValue="Allotments"><i className="fa fa-plane fa-fw"></i>Allotments</DropdownItem>
        <DropdownItem onClick={this.onDropdownItem_Click} dropDownValue="GeoAMS"><i className="fa fa-envelope fa-fw"></i>GeoAMS</DropdownItem>
        <DropdownItem onClick={this.onDropdownItem_Click} dropDownValue="QIS"><i className="fa fa-money fa-fw"></i>BSP</DropdownItem>
        <DropdownItem onClick={this.onDropdownItem_Click} dropDownValue="QIS"><i className="fa fa-clock-o fa-fw"></i>QIS</DropdownItem>
        <DropdownItem onClick={this.onDropdownItem_Click} dropDownValue="NO_SHOW"><i className="fa fa-car fa-fw"></i>NO SHOW</DropdownItem>
      </DropdownMenu>
    </Dropdown>
}

Add an onclick on your DropDownItem (inside a div ?) to change your state. Set a "dropDownValue" from your click event. In your dropDownToggle, get your state.dropDownValue.

Something like this :

changeValue(e) {
  this.setState({dropDownValue: e.currentTarget.textContent})
}

<DropdownToggle caret>
    {this.state.dropDownValue}
</DropdownToggle>
<DropdownItem>
    <div onClick={this.changeValue}>Another Action</div>
</DropdownItem>

Of course, don't forget to init it and bind the function for your this to work.