Music doesn't only happen in the studio. If you want to be ready to record the tunes wherever they happen, a portable or field recorder is an invaluable piece of equipment to have with you. Today's handheld recorders aren't the unwieldy tape machines they once were – now that they're all digital, they can deliver amazing sound quality that would have required a whole recording booth's worth of gear in the past. If that's not enough for your needs, you can step up to a portable desktop recorder that will give you quality and connectivity comparable to full-fledged studio units, but in a size and weight that's easy to transport.
The smaller handheld field recorders put their emphasis on simple control layouts that are as easy as possible to learn and use, which is perfect for times when you need to start recording on short notice to avoid missing a beat. Some are designed specifically for certain instruments, such as the TASCAM GT-R1 for guitar and bass. As well, a handheld recorder is right at home at a jam session with bandmates, where you can use it to record as you develop the riffs for your next song. They're also great for recording spur-of-the-moment lyric ideas or even just taking memos for yourself. For a fully-featured mobile studio, take a look at the desktop portable recorders like the TASCAM HD-P2 or the Fostex FR-2LE. Since they're bigger than handheld recorders, they have room for XLR inputs that allow you to connect your own professional microphones or sound units.