"Technology...the knack of so arranging the world that we don't have to experience it." — Max Frisch
The electronic accessories will (literally) make or break the ability of your fieldwork technologies to work.
One must onsider electrical grid plugs, conversions, and accessory cables, converters, adapters.
Adapters change the plugs only, converters step up or down the voltage, and transformers are like converters for more sensitive or permanent applications. Most modern electronic devices accept multiple voltage inputs, so oftentimes you really need to focus just on the adapters. I like to throw this
Electricity networks are not all created equal, and you'll want to anticipate power fluctuations, outages, and spikes.
Surge protectors are a must—and recognize that many generic chargers are unreliable and can shorten the lifespan of your devices. There are good international surge protectors out there as well
Some newer surge protectors have USB plugs which can be a nice convenience.
Finally, also pay attention to the wattage capacity chargers for computers, tablets, and phones. Standard phone chargers take a long time to charge a tablet.
Depending on your location, a separate solar charger/panel may be a good investment as well, allowing for even more flexibility (particularly if you're worried about emergency safety-and-security concerns, as one ought to be).
When evaluating solar chargers, some of the main components you'll want to think about include: size and portability (stowed versus charging), wattage produced (higher means more charging potential), and ruggedness.
Batteries and power banks
An external battery is a must-have these days for prolonging useful hours of work between power grid opportunities. I'm a fan of the small, and medium solutions out there, but haven't had much experience with the larger sized banks capable of charging laptops.
In order to get all of these devices to talk to each other, be sure to bring all of the relevant cables/chargers/cords for these devices.
It's worth it as well to consider getting 'braided' cables which hold up a little longer in rugged environments. I'm a big fan of using the shortened cable version of connectors as they don't tangle as easily.
Additionally, you would be doing yourself a favor in investing in a quality USB charger, rather than relying on the often-times knock-off brands you will find in country which are not as solidly built and might contribute to your device shorting out.
External hard drives are critical in being able to keep backups of your work and projects. They pay for themselves in peace-of-mind alone when traveling with your laptop across the country and to be able to share files.
It's worth it to consider bringing both a portable external hard drive as well as a few high-capacity USB stick (thumb) drives (like these) for swapping files and material with colleagues as needed.
I normally think that 'ruggedized' as a feature is just buzz marketing, but I do like the extra padding on these, so you might want to consider the value of losing your data through travels, jostling, and the elements.
USB modems (also called more generally 'dongles') are the USB sticks that plug into your computer's USB port and allow it to communicate with local data and cellular plans.
It might be a good idea to purchase a USB modem for personal and professional use in-country. Like mobile phones, these devices can be 'locked' to specific carriers, or bought already unlocked -- though pay attention to GSM v. CDMA v. LTE technologies as you would with mobile phones.
Finally, you'll want to weigh carefully the various technologies and communications of modems—they can be sold in USB form, router form (requiring power), with/without Wi-Fi connectivity, etc.
For modems, pay close attention to various contract obligations (typically pay-as-you-go or monthly plans), rate plans, upfront purchase costs, and the stated versus real coverage area of the various service providers (this may take a few days/weeks to figure out). Don't forget to pay close attention to stated versus actual speeds (2G, 3G, 3G+, 4G, LTE, etc.), as this affects performance (and frustration) significantly.
If you're looking to get advanced into networking and connectivity, I highly reccomend the Wireless Network in Developing World book. It's a guide to designing and building wireless networks in local communities, enhancing lives through improved communication, access to information for educational, social and economic growth.
Having a wireless router can allow you to create a local wifi network in order to share files and connect to local devices. Paired with a USB modem, you can create an on-the-fly mobile hotspot.
Flashlights and headlamps
Flashlights and lanterns can be very useful too, depending on what your environment will be like, though I have less personal experience with these myself. For flashlights, I know that a lot of folks swear by the FourSevens models, but their specialized battery requirement has always turned me off. For lanterns, I know someone who swears by having portable, rechargable, collapsable models, but I haven't played with it much.
Noise-cancelling headphones are a lot cheaper and easier to come by these days, so I would recommend looking into a pair for travel and long flights. Don't forget to bring some cheap backups (though doubly don't forget that you can find replacements in country as well—just maybe not your preferred brand and fit.)
I'm also a huge fan of bluetooth headphones so that I can listen and charge / be mobile at the same time.
Now, I wouldn't normally include this here, and it's going to be a little more challenging to get through international travel and customs, but I love the idea of the BioLite Cookstove that allows you to charge a battery and your devices from a fire. I've only seen it used, and I wasn't able to tell how effective it was, so let that be a disclaimer.
Faraday cages and RFID blockers
Faraday cages block all cellular, Wi-Fi, and radio signals and can be sewn into carrying cases and portable pouches. RFID blockers do the same thing, but specifically blocking RFID signals. Good if you're worried about having your credit card / cellphone data skimmed.
I haven't had a chance to use a bluetooth tracker, but I've heard good things about being able to use them to track your belongings and rest a little more assured that they are in your proximity.