For software distribution tapes, I'd recommend VMSTPC, and make tape images.
For data, it becomes a bit more interesting, but I'd still recommend making
images with VMSTPC, and you'll most likely also want to take a look at the
lddriver suggestion and make your own CD's.
The question really becomes in what form do you want to access this data in
the future. If you make TPC images of the tapes, you can then either copy
them back to tapes at some point in the future, or use one of the SIMH tools
to turn it into a SIMH TAP file.
Zane