I have a laptop and portable scanner which works pretty well. I have a Brother DS620 which scans 8 pages per minute in color or B/W and the clarity is solid. I will usually use this for a seller signing far enough away from my house that it would cause the title company agita if I drive home then scan.
For a job with only a few docs to scan back (like a reverse app) I use the Scannable app on my iPad. It works great, and links with Evernote to allow me to convert to PDF and email.
Any more than that and I will wait until I get home to use my desktop scanner.