<form>
        <label>Variavel</label>
        <select name="variavel" id="variavel">
            <option value="1">Variavel 1</option>
            <option value="2">Variavel 2</option>
            <option value="3">Variavel 3</option>
            <option value="4">Variavel 4</option>
            <option value="5">Variavel 5</option>
            <option value="6">Variavel 6</option>
            <option value="7">Variavel 7</option>
            <option value="8">Variavel 8</option>
            <option value="9">Variavel 9</option>
        </select>
</form>

<script>
    recentes = new Array();
    var salvarVariavel = function()
    {
        var variavel = document.getElementById('variavel').value;
        var v = localStorage.getItem("recentes");

        recentes.push(variavel);
        localStorage.setItem("recentes", recentes);
    }
    document.onchange = salvarVariavel;
</script>