Instead of interpolating(using {{}}) something in the ng-bind directive you can simply enclose the filtered value with a parenthesis and append your text.
<h1 ng-bind="(input | filter) + ' more stuff'"></h1>
furthermore, if the text you want to add is not in any way dynamic then I suggest you append another element to bind the filtered value and then add the text after that element.
e.g.
<h1><span ng-bind="(input | filter)"></span> more stuff</h1>
This saves you one concatenation process.
Example here