I was planning on giving user an option to upload files while answering a survey. Is it possible to attach an item to a survey list ?
if not, use a custom list ;)
This may not be an ideal answer; but since surveys are not easily customizable, and a custom list doesn't behave exactly like a survey, you might try this:
Just add a lookup column to survey that fetches docs in doc library. Include the survey response number - or other unique survey response identifier - in the doc title. But then a case of scrolling through the small lookup display (on the survey response edit form) to select matching document
In SharePoint 2013, you can select the External Data type to specify what types of files you want to upload when you create each question. The hitch is that your administrator has to have enabled External Content Types or you will not have permissions to create an upload feature as part of the survey.