{"beverages":["Coffee","Coke"],"snacks":["Chips","Cookies"]}

<script type="application/javascript">
$("#first-choice").change(function() {

    var $dropdown = $(this);

    $.getJSON("../../getdata.php?getDropdown=yes&people_no=1", function(data) {

        var key = $dropdown.val();
        var vals = [];

        switch(key) {
            case 'beverages':
                vals = data.beverages;
                break;
            case 'snacks':
                vals = data.snacks;
                break;
            case 'base':
                vals = ['Please choose from above'];
        }

        var $secondChoice = $("#second-choice");
        $secondChoice.empty();
        $.each(vals, function(index, value) {
            $secondChoice("<option>" + value + "</option>");
        });

    });
});
</script>

<select id="first-choice">
    <option selected value="base">Please Select</option>
    <option value="beverages">Beverages</option>
    <option value="snacks">Snacks</option>
</select>

<br />

<select id="second-choice">
    <option>Please choose from above</option>
</select>

vals = data.beverages;

$secondChoice.append("<option>" + value + "</option>");