Mostly binary dependencies. Some are executable files (for instance, GRUB Stages 1 & 2), some are DLLs, and some are redistributables.

Reason they're under SCM is because we maintain some of them; with varying degrees of changes. Some have their own repositories, naturally, but others involve minor changes and/or just simply take too long to build. And for some of the redistributables: we don't have the source code for them in the first place.

Images and MS Office documents. If you do anything with MS Access then the program itself is stored in a binary file.