What temporary files can I safely delete?

SOLVED

In preparation for a migration (and also to reduce backup size, etc) and know I can safely delete .old, .bak and WRK files. I find there are a TON of files in the MAS90/Reports folder, most of them we do not use.

1. What are rp_ files and can I delete them?

2. Is there listing somewhere of standard reports that SHOULD be in this folder, so I can remove old junk we created and then forgot, without danger of deleting a standard report I should really leave in place? 

2. What other temporary files can be safely deleted?

Thanks.