The Content Basket component uses the ZIP Rendition Management to package the contents of the basket for download as a ZIP file. By default there are two limitations imposed on your download. It must be a count of five hundred (500) pieces of content or less and it must be a total of five hundred (500) megabytes or less. The two settings that control this are actually part of ZIP Rendition Management and not Content Basket.
This variable represents the max size in megabytes (default is 500 megabytes). From the internal notes: Note, it is unlikely that a browser + web server will successfully download a file over 2 gigabytes over 2 gigabytes and you need 8 byte integers in the Content-Length HTTP header) in all scenarios so the effective maximum cap on this value is 2000 megabytes.
This is the max number of items available to package in the bundle.