Windows: If you have a spare USB drive or SD card lying around, use RMPrepUSB to turn it into a PC troubleshooting tool or a way to install a new OS without burning a disc. You can use the tool to format and partition any storage device, load it up with ISOs or other disk images, and then multi-boot when you need to.
RMPrepUSB is free, and once installed on your PC, you can use it to turn USB thumb drives, hard drives, SD cards or almost any external storage into partitioned, bootable media that either loads an ISO or boots to a fully installed partition on the drive. You can also use it with drive images, so you can boot to or install backup images of your PC in case there's trouble. The app has a lot of features, most of which you can check out here.
The tool supports grub4dos and easy2boot, so you can load up Linux ISOs, Windows ISOS, install Linux right to the USB drive or customise a Windows partition, then just plug the drive into your PC to boot directly to it like it was an internal drive. Keep in mind that while RMPrepUSB will prep and partition your USB drive to be bootable media, you still have to have the operating systems you want to boot to and the images you want to load the drive partitions with.
It makes the job easier, but it doesn't do everything for you. For examples of what the app can do, check out some of the app's video tutorials, which guide you through using easy2boot to add Windows partitions, using the app to build a USB version of the Ultimate Boot CD for troubleshooting and more. Thanks Whiznot2!