jQuery toggle buttons to show matching content in sliding panel
In the click event we will see right away from reading the if statement that you are performing a check to see if the slidingPanel is open by looking for a class of open on the element, so get rid of that first comment, you should also got rid of the //if slider is close, open slider  because that is also obvious from reading the code.  I am unsure of The final comment so I won't make a judgment on it.

Remove the return statement and make it into an if/else statement, because that is essentially what you are doing and it will read nicer.

This is what it turns into

var slidingPanel = $('#sliding-panel');
$(body).on('click', '[data-toggle="slidingPanel"]', function() {
    if(slidingPanel.hasClass('open')){
        slidingPanel.hide("slide", { direction: "right" }, 500).removeClass('open');
        $('.buttonContent').hide();
    } else {
        slidingPanel.show("slide", { direction: "right" }, 500).addClass('open');
        //show content in slider based on button pressed
        $('#' + $(this).attr('id') + 'content').show();
    }
});