In addition to what yaspr said, i'd suggest looking for specification of those contained files. Most file formats have their size specified in the header somewhere. That would allow you to carve the file from the archive, without even knowing the archive structure.
This is what tools like
scalpel are doing to carve files. They match the header to a known file type, and then lookup the file size in that header.
Some file formats have specific endings which you could also use to carve them out (for example, every
png file has
IEND and the end).
Try your luck with
scalpel and similar file carving tools.