Set Additional Data to highcharts series

Yes, if you set up the series object like the following, where each data point is a hash, then you can pass extra values:

new Highcharts.Chart( {
    ...,
    series: [ {
        name: 'Foo',
        data: [
            {
                y : 3,
                myData : 'firstPoint'
            },
            {
                y : 7,
                myData : 'secondPoint'
            },
            {
                y : 1,
                myData : 'thirdPoint'
            }
        ]
    } ]
} );

In your tooltip you can access it via the "point" attribute of the object passed in:

tooltip: {
    formatter: function() {
        return 'Extra data: <b>' + this.point.myData + '</b>';
    }
}

Full example here: https://jsfiddle.net/burwelldesigns/jeoL5y7s/

Additionally, with this solution, you can even put multiple data as much as you want :

tooltip: {
    formatter: function () {
        return 'Extra data: <b>' + this.point.myData + '</b><br> Another Data: <b>' + this.point.myOtherData + '</b>';
    }
},

series: [{
    name: 'Foo',
    data: [{
        y: 3,
        myData: 'firstPoint',
        myOtherData: 'Other first data'
    }, {
        y: 7,
        myData: 'secondPoint',
        myOtherData: 'Other second data'
    }, {
        y: 1,
        myData: 'thirdPoint',
        myOtherData: 'Other third data'
    }]
}]

Thank you Nick.