What every IT Guy tends to keep, however, is a cache of essential utilities that he/she use with them all the time. As you become more tuned to the kinds of utilities you use, you’ll find ways to make them more available to yourself when you are at the client (at a moments notice).
Nirsoft has a great history of making utilities, these are free and very useful. Just today, Nirsoft released a new one that, as he says he “created this utility within a few days without planning to create it before”. I like it!