While Bundler app doesn't yet natively have an option to set some kind of a tick box in the bundle itself, you can add one or more simply through our JavaScript API. 

To add any element to a bundle widget (including a tick box), just create a JavaScript code, which will listen to “bundler:bundle_widget_created” event and then inject the line item properties into each product box separately. Here is a sample code on how you can add line item properties to the widget:

// This event will be fired whenever a bundle widget is rendered
document.addEventListener('bundler:bundle_widget_created', function(e) {
    document.querySelectorAll('.bndlr-product').forEach(function(el, index) {
        el.innerHTML += '<input name="properties[custom_property]" type="hidden" value="custom property value" />';
    });
});

You can read more about this in our JavaScript API documentation: https://bundler.app/javascript-api-documentation