Some links below are Amazon ad affiliate links but I only recommend products I have actually used and tested. It does not cost you any extra but it helps to earn me a few pennies…
USB drives should have a metal shroud around the USB connector. If you use a USB drive that has a plastic shroud or no shroud, then you will get connectivity problems on some computers (don’t ask me how I know!).
Always buy a USB 3 drive as they will be much faster than USB 2 drives even if you only have a USB 2 port available.
USB Flash drives (Removable type)

Sandisk Extreme Pro USB 3.1 (Gen 1) CZ880 (#Amazon ad link) (review) Fast and most compatible
Transcend JetFlash 920 (#Amazon ad link) (review)
USB Flash drives (Fixed/Hard Disk type)
Silverstone 2242 M.2 SATA III SSD to USB 3.1 Gen 2 Enclosure with Retractable (SST-MS09C-MINI) – add M.2 card for superfast USB!
USB HDD/SSD (Fixed)
For USB booting I recommend using a USB 3.0 enclosure (not USB 3.1 or 3.2) and an SSD drive (lower power requirement than HDD, more robust, no spin-up delay).
USB CD\DVD Emulator
IODD range – e.g. The IODD Mini SSD (recommended) also supports encryption. Can emulate Removable or Fixed USB drive. Can be write-protected.
IODD’s can be loaded with 100’s of ISOs and VHD files. You can then load one or more of these via the IODD controls to emulate a CD\DVD\Removable drive\Fixed drive.
USB Flash Encrypted
Accessories
USB 3 Y-cable – Useful when using USB HDD with higher power requirements
USB 2 extension cable – Use between USB 3 port and USB 3 drive to force system to use USB 2 protocol and drivers. Do NOT buy a USB 3 cable (USB3 has blue connectors!).
Note: Buy good quality shielded USB cables with metal USB shrouds around each connector.