How to boot multiple operating systems on one usb drive?

To successfully boot multiple operating systems on one usb drive, start with a high-quality USB 3.0 or 3.1 drive. Operating systems involve moving massive amounts of data; using an older USB 2.0 stick will result in agonizingly slow boot times and potential timeouts during installation. Aim for at least 32GB of space so you have room for multiple installers and a dedicated partition for personal files.

Before booting, enter your computer's BIOS/UEFI settings and disable Secure Boot. While some tools like Ventooy offer workarounds, Secure Boot is the most common reason a multiboot menu fails to load. Additionally, ensure your "Boot Priority" is set to check USB devices first so you don't bypass your drive and head straight into your primary OS.

Pay close attention to UEFI vs. Legacy (BIOS) modes. Most modern computers use UEFI, but older machines require Legacy support. 

Finally, always test your drive on a secondary machine or a virtual machine before relying on it for an emergency. It is much easier to troubleshoot a "File Not Found" error or a corrupted ISO while you still have a working computer and internet access. Keep a "clean" copy of a Windows installer and a lightweight Linux distro like Lubuntu as your reliable fallbacks.