Sometimes the key to being a good consultant is having the right tools at the right time. There are a lot of tools out there, some complex and some simple and straightforward that I use on a regular basis.
One of the easiest ways to carry tools around is on a USB flash drive. There are many self contained executable programs out there that will run off of a USB flash drive enabling you to use them on the go. This is especially handy to the consultant that is always on the move.
One of the simple suites of apps I like to carry around on my USB flash drive are from PortableApps.com. There you can find a lot of nice useful apps for your flash drive.