2.1 x 5.5mm paired DC Barrel Connectors
TRS "Phono" Connectors - these are really useful for building test cables or attaching a rig interface to the ADC port on an Arduino or ESP8266. When you get to the mountain for a SOTA activation and realize your 5 year-old has yanked the end off your headphones, you'll want one of these.
1/8" (3.5mm) Tip-Ring-Sleeve "phono male" plug
1/8" (3.5mm) Tip-Ring-Sleeve "phono female" jack
For pocket tools, I prefer the Leatherman ES4 Squirt. (http://amzn.to/2bEe5lV) It's a ham's dream tool, with a wire stripping jaw, knife, scissors, file, and a screwdriver bit that works well on these screw terminal adapters.
Other interesting stuff....
BNC Female w/ screw terminal - these are 75 ohm, designed for CCTV installs, but for receiver testing or low-power transmit they'll work OK. Be aware that some adapters like this actually have baluns, which you don't want for RF testing.
RJ45 screw terminal plug - kinda bulky, but it's great for designing cables on a bench. When I'm done and have a working design, I build a real cable using CAT6 and an RJ45 crimper or a punch-down terminal block.