Problem:
You have multiple ongoing projects in Maptionnaire, and now the Materials section is full of images, map layers and documents from all of them.
Solution:
Tag your materials! You can give each image, map file, document and audio file a tag. Then, when you are putting together a survey or a page, you can just use the tag to bring up all the different files related to that specific project.
In Materials, you can look up what files you have already added for the project by filtering by tag.
When building a survey / page, you can simply pick a tag...
...and the drop-down menu will only show files that share that tag.