Squarespace has good forms builder, but unfortunately there is no upload field to store user files or docs. It may be useful for user images, screenshots, pdf-forms or so. Sure you may use some side services to organize file uploading: Wufoo, JotForm and many others. And while they have great builders and file uploads, sometimes you need more than 3-5 forms or 1000 form views per month with free account. So we decided to make a small javascript plugin, which adds file upload fields to Squarespace forms and small service to handle these uploads.
Squarespace has a variety of fonts available out-of-box. There are many Google and Typekit fonts to choose from. You can even add your own Webfonts fromTypekit or other 3rd part font providers but more often than not, you will need to add custom fonts to make them available for choosing in Style Editor, which is actually an important consideration.
Sometimes you just need to add search to your site. It is simple to do with usual Squarespace Search Block. This way works for pages, collection items and editable blocks in template.
Popular question on Squarespace Answers is about adding some background music to page. This is not the best UX to autoplay something on pageload, but we may give a try.