This is a different flavor of posting. For the past couple years I've been on the road a lot and built a collection of useful gadgets to have on a trip. So here is a product recommendation posting. There might be better alternatives, but these are all items I use on my trips every week. As they say, your mileage may vary. (If you don't want to read a product list, just skip to this post instead.) I'll get back to technical posting next time.
USB charging protector so that when you plug into a rental car it doesn't try to download your phone book, airplanes don't try to connect to your tablet file system, etc. Or worse, actually attack your phone via juice jacking. This one also supports at least some phone fast charge signals so you get the quick charge rate. Lots of people use a "c" word to describe this, but better to avoid it to keep the blog safe for mindless nanny filters.
PortaPow USB Block
Travel wireless router. Input can be wired Ethernet or hotel WiFi. Output is a Wifi signal that you can use for your multiple devices. Handy if you want to pay for one internet connection at a hotel and share with multiple devices. Arguably provides a little more security due to built-in NAT (but not bulletproof). It takes a couple minutes to set it up on a new location, but pretty painless once set up.
ASUS Pocket Router
Power plug adapter. Universal international power adapter that works in every plug I've ever seen. It's super clever. (It is a plug adapter, not a voltage transformer.)
Kikkerland UL03 Power Adapter
USB AC charger. Travel size USB power modules so you can keep one in your suitcase. Slightly bigger than the official Apple ones, but a lot cheaper. 110/220V compatible.
Over-ear noise cancelling headset. Yes, this is the one you always see on frequent travelers. It really does make a difference in reduce wear and tear on your mind from the constant low-frequency roar of jet engines. You can still hear people talking (although it is reduced; I pull back one ear when talking to a flight attendant). Gets multiple flights out of a single AAA battery (if you remember to turn it off before you stow it). The one I got came with an iPhone cable so you can also use it for phone calls (or skype) home from a somewhat noisy location. I like the ones like these that have full ear "cans" that fully cover the ear so they provide noise reduction even when turned off.
Bose QC 15
I see that these are now discontinued, and I don't have an opinion on newer models, but generally I've had good luck with Bose headsets so probably the newer one is fine too. (Bose QC 25)
Laser pointer and slide advance. Bright green laser pointer, forward/backward buttons for slides shows, and a built-in timer. I use this every week.
The charger electronics are the "cheap" type which might have random build quality, but none of the above have given me any problems after significant use.
Computer travel backpack. This is the best backpack I have used for laptop and other stuff. The top zippered compartment is way more useful than I had expected. Very durable. Love it. I see it all the time on other frequent business travelers.
SwissGear Blue Ibex backpack
Semi-disposable canvas bags. Medium-weight drawstring "beach backpack" bags. Use for light groceries when they charge for bags at checkout, keeping your stuff together if you have your backpack in the overhead, keeping your pillow clean if you need to stash it on an airplane, dirty laundry, etc. Folds up to be pretty small. (No doubt plastic ones would fold up smaller, but I like the canvas fabric in this one). About $3 apiece but you need to buy a dozen at a time. Alternately bring your favorite beach backpack.
Miscellany bags. Durable small zippered bags to carry USB cables, chargers, tea bags, and so on.
Ergonomic Travel Pillow
Travel liquid containers. Small and easy to squeeze silicone bottles. Great for shampoo, skin lotion, sunscreen. Get the 1.25 oz size for carry-on. They are color coded (mine are green, blue, pink).
If you like 3-D printing then I recommend the following free designs:
One-piece business card holder: http://www.thingiverse.com/thing:31281
Card case for holding assorted cards not in your wallet: http://www.thingiverse.com/thing:66327
Travel battery holders (I travel with two AA and four AAA): http://www.thingiverse.com/thing:57281
Cable clip for USB cables: https://www.thingiverse.com/thing:69983
Travel-size toothpaste refill adapter: http://www.thingiverse.com/thing:158910
All of the above will no doubt require the usual fiddling with scaling, but I've found them very useful once I get them the way I like them.
Finally, there is the stress of dealing with the rental car collision coverage dilemma. Do you buy the expen$ive daily collision waiver from the rental company? If you don't, do you really believe your company will pay out if there is rental car damage? (Depends on your company I'm sure, but I've heard stories of this not working out well.) Or do you take your chances and hope it comes out OK?
For a couple decades now I've carried a Diners Club personal card that comes with primary collision insurance if you use it to pay for the car rental. The US flavor of Diners Club is now just a particular bank logo on an ordinary Mastercard, so acceptance isn't an issue. I've had to use the insurance twice over the years (minor car damage while parked) and no muss, no fuss. They just took care of it with no deductible. There are various other cards with various deals. The thing to look for is "primary" (first-payer) coverage. Your other credit card may say it covers rentals, but most of them are "secondary" and thus only pay what's left after your personal car insurance takes care of most of it and you take the hit to your insurance premiums. I've found that hotel parking lots are particularly dangerous places for scratch-and-dent damage, so worth looking into this.
Here's a good list of credit cards useful for this (I get no compensation from this referral):
Most come with annual fee or per-use fee, but if you rent even a few days a year it pays off quickly. Of course it is important to pay attention to which locations are covered if you're traveling away from your home country.