There's a reason the phrase "you don't know what you have till it's gone" exists. It's unlikely, however, that was originally coined when talking about electricity, but these days, keeping mobile devices charged is of paramount importance for business travelers. When it comes to keeping your smartphone, tablet, and laptop adequately juiced, it's worth planning ahead.
Even if you think you have the logistics worked out in your head, unforeseen issues can crop up that would prevent you from meeting the AC outlet as you had planned. Whether it's aircraft changes, flight delays, or an airline lounge being closed for renovations, if you aren't prepared, hiccups such as these can leave you high and dry when it comes to battery life.
For iPhone and Galaxy S III owners, I'd strongly recommend investing in a Mophie case. The company has a short, but proud heritage of providing exceptionally well-built cases for high profile smartphones. But, unlike most plastic shells, these cases also include a built-in battery pack, easily doubling the lifespan of the phone which they envelop. So long as you charge it before leaving the house, you'll be able to tap into that juice with the flip of a switch.
It's also worth tossing an Energizer XP2000 Universal Rechargeable Power Pack into your carry-on. This unit is barely larger than a deck of cards, but it packs a built-in battery and a USB port, enabling you to tap into emergency power for recharging your BlackBerry, iPhone, Android phone, tablet, or any other USB-powered product. It also ships with a handy carry case and a variety of tips to support a plethora of handheld products.
If you travel with a Mac laptop, consider purchasing a HyperJuice. Put simply, these are highly dense batteries that are capable of powering some of your most vital tools for hours on end. The larger, more expensive units can power MacBook laptops for well over 12 hours, while simultaneously charging any other USB-based product like a smartphone or tablet. You could easily work through a full day using this alone for power, which also makes it great to keep in the home in case of power outages there (lest you think that's not an issue, thousands of people were left without power for more than two weeks after Hurricane Sandy).
With all of these solutions, it's hugely important to keep them all charged up ahead of time. Once you need them, it will likely be too late to charge them.