Law practice management [LPM] software is often cloud based which can be a good fit for a mobile office. Most tend to offer a variety of functions that integrate with each other, including contact management, calendar, task lists, matter/engagement management, time sheets, time capture, billing/invoicing, and more.
You can associate (upload) key documents and communications (emails) with matters, a good way to keep things organized and accessible. Major providers include Clio and RocketMatter. Lexis and many other companies also offer LPM products.