There is no good way to see the contents of FormData. A trick would be to send it (POST) and look at the network status.
Example: http://jsfiddle.net/K7aMw/2/
$(document).on("click", "button", function (e) {
e.preventDefault();
var inputs = $("#my_form input");
$.each(inputs, function (obj, v) {
var file = v.files[0];
var filename = $(v).attr("data-filename");
var name = $(v).attr("id");
myFormData.append(name, file, filename);
});
var xhr = new XMLHttpRequest;
xhr.open('POST', '/echo/html/', true);
xhr.send(myFormData);
});
Then in the Network tab (F12) you'll see the added files when inspecting the headers.