I am not sure if you need password recovery or not, but it looks like this is well covered. If your plan is to straight resell these at auction, then I would look at the following:
Go onto the router (pw recover if need be) and type "write erase" enter that command, and then "reload" the router - when it comes up it should be at "factory default" as far as configuration goes.
Once it is back up, you need to go onto the router console and do a "show version" and record the RAM/Flash, this will be critical information to anyone buying it. There will be some lines similar, but not exactly, like this:
cisco AS2511-RJ (68030) processor (revision K) with 14336K/2048K bytes of memory. (16M RAM)
8192K bytes of processor board System flash (Read ONLY) (8M FLASH)
I added the RAM/FLASH numbers in paranthesis.
Next, like the other user mentioned, you either need to include a console cable (rolled Ethernet by the way - may or may not be blue depending on when they bought the 2600) or state that there is no Console cable. Depending who is buying it, they may have no need of one (I have about a thousand hanging around for example). You should also mention whether or not rack mounting brackets are included or not - these can be expensive to buy from Cisco, so you need to let someone know upfront what they are getting.
As to software, you can find that out from the "show version" output as well, near the top:
Version 11.2(23)P
If it is a cryptographic image (there will be a huge disclaimer in the output if this is the case) then you may have legal ramifications as far as where is exports to. I would not change the software, it is not free.
A caveat to all of this is you may want to check on CCO that the equipment is not "black listed" somehow, if it is then the buyer may NEVER be able to register it or get support for it.