1. Laptop power cord Panic. That is the feeling that hits you when you arrive at a destination and realize you forgot to pack the power cord for your laptop. Without it, you have mere hours of productivity before your laptop will die, and you'll be dead in the water. If possible, you should have a spare power cord that is always in your laptop bag so you don't run the risk of forgetting to bring one. If you can swap out the battery on your laptop, you might want to carry a spare battery as well.
2. Smartphone / tablet charger Along those same lines, you also don't want to embark on a business trip without the adapter and/or cable you need to recharge your smartphone or tablet. Ideally, you should have a backup always stored in your laptop bag for the same reason cited above.
3. USB flash drive USB flash drives seem like they're already on their way to obsolescence, but they still come in handy in a pinch. If a customer or vendor needs to share a file with you, or vice versa, a USB flash drive is often the most convenient and efficient means available.
4. Portable hard driveFor laptops with smaller SSD storage, an external USB hard drivemay be necessary just to store and transport data you need without filling up the storage on your laptop. It's a good idea to have a portable hard drive in your laptop bag in general, though. You can use it to carry the crucial software you rely on in case you need to reinstall it, or you may need to back up your laptop or store a file that's simply too large for a USB flash drive.
5. Ethernet cable There are times when you're traveling that an Ethernet cable comes in handy. Most hotels offer wireless network access, but it's often flaky and unreliable, and some hotels have wired Internet access, but no wireless network. You also may need to connect to a network at a customer or vendor site. An Ethernet cable is inexpensive, and could be a lifesaver when traveling.
6. 4G hotspot Another option for connecting on the go is to have your own 4G hotspot. You can use a dedicated 4G hotspot device, or share out the cellular connection from a smartphone or tablet to allow you to get connected and get stuff done on your laptop from virtually anywhere.
7. Headphones Whether you want to catch up on season 2 of Portlandia during your flight, or listen to some music while you work in your hotel room, you should have some headphones in your laptop bag. You can use a simple pair of earbuds if you want some headphones that take up little space and weigh next to nothing, or you can use some larger, higher quality headphones that generally have better sound and do a better job of blocking out other noises around you.
8. Pain medication This is not a gadget, but it's a must-have for traveling. Headaches tend to strike at the least convenient time possible, and purchasing a Tylenol or Advil from the store in a hotel lobby is often quite expensive. You should have a travel container or your pain medication of choice available.
9. Coffee This is also not technical, but vitally important for coffee drinkers. In case there isn't a Starbucks available, and the mediocre coffee from the miniature pot on the bathroom counter in the hotel isn't cutting it, you should carry around a stash of Starbucks Via packets. I have an assortment in my laptop bag, including coffee, iced coffee, and the Very Berry Hibiscus Refresher drink.
10. Business cards The concept is a little "yesterday", but people do still exchange business cards. Sure, it seems simpler and more efficient to just add contact info to your smartphone or tablet since you're going to have to do that anyway with the information from the business card, but you've got the cards so you may as well use them.
Some of these things may never even be used, but Murphy's Law suggests that the one time you travel without them is the one time you will really need it. So, stock your laptop bag now, and be prepared.