Honestly, I think the ability to link an external URL as a handout would be more than enough. Then you can stick a PDF on Dropbox and link to it, provide a Google Spreadsheet template for your character sheets, link to a Google Docs file, link to an Evernote page, or whatever.
As background, my group has used shared Evernote notebooks to keep the master reference copies of character sheets in place, as well as functioning as a sort of wiki of information the GM adds or players make notes of. (This is true of our in-person games as well as online ones.) So external URLs as handouts would sync nicely with our existing process. :)
That really down to it is all that is need. I pull my player's characters from having a shared Google Docs sheet per character and that works well. When trying that with a test of d20 in Google Hangouts, it was anything but as efficient as I wanted. I just ran a quick test, I ran my campaign in Google Hangouts, then added the Google Docs App and it forces me to go back in forth between the two rather than layering one with another.
If we could pull an external link into d20Roll then it will let the DM's / Player's choose a format that they are comfortable with, either it be a PDF, Google Spreadsheet, ect...
Keep it going, guys, still some great thoughts being bounced around here. I'm just off to check out including URLs in characters and possibly handouts.
Just to reiterate:
I do NOT:
a) Require the material to be stored in the Roll20 database
b) Require to be able to edit the material within Roll20
a) Require to be able to access the material with a single click on something (icon, hyperlink, button, whatever) that IS within Roll20.
I think your requirement is perfect!