Script for Google Forms. Uses "Other" field in checkbox and radio groups to add options from responses.

Google_forms_other.gs

/*
Script for Google Forms.

"Fixes" other... field in checkbox and radio groups.

Whenever form is submitted and "other" option is selected, 
input goes to corresponding checkbox/radio group in form 
as a new option, so next respondents don't have to put it
in manually.

To use copy-paste code to your forms project and assign 
onSubmit function to project's "on form submit" trigger.

By default applies to all checkbox/radio groups in the 
form, specify required IDs in applyOnlyTo if needed.
Normally it is in "data-item-id" field and numeric only.
E.g. data-item-id="193574675"
*/

function onSubmit(event) {
  var applyOnlyTo = []; // fill this in if you want descibed behaviour only for selected checkbox/radio groups;

  var form = event.source;
  var response= event.response; 
  var choosers;
  
  if (applyOnlyTo.length > 0) {
    choosers = applyOnlyTo.map(function(id) {
      return form.getItemById(id);
    });
  } else {
    var checkboxes = form.getItems(FormApp.ItemType.CHECKBOX);
    var radios = form.getItems(FormApp.ItemType.MULTIPLE_CHOICE);
    choosers = checkboxes.concat(radios);
  }
  
  choosers.filter(function(c) {
    var type = c.getType();
    return (type == FormApp.ItemType.CHECKBOX) ? c.asCheckboxItem().hasOtherOption():
           (type == FormApp.ItemType.MULTIPLE_CHOICE) ? c.asMultipleChoiceItem().hasOtherOption():
           false;
  }); 
  
  for (var i = 0; i < choosers.length; i++) {
    var chooser = choosers[i];
    chooser = (chooser.getType() == FormApp.ItemType.CHECKBOX) ? chooser.asCheckboxItem():
              (chooser.getType() == FormApp.ItemType.MULTIPLE_CHOICE) ? chooser.asMultipleChoiceItem():
              "Something went wrong. It is definitely Google's fault!";  
   
    var chooserResponse = response.getResponseForItem(choosers[i]);
    if (chooserResponse == null) continue;
    
    chooserResponse = chooserResponse.getResponse();
    var otherField = (chooser.getType() == FormApp.ItemType.CHECKBOX)?
                     chooserResponse[chooserResponse.length-1]:
                     chooserResponse;
    
    var choices = chooser.getChoices();
    
    if (!mContains(choices, otherField)) {
      var newChoice = chooser.createChoice(otherField);
      choices.push(newChoice);
      chooser.setChoices(choices);
    } 
  }
  
}

function mContains(choices, item) {
  for (var i = 0; i < choices.length; i++) {
    if (choices[i].getValue() == item) {return true;}
  }
  return false;
}