I, too, have learned the hard way to carry backups and check the gear carefully. I drove 165 miles to a nearby state only to learn I'd left the PA head! Fortunately, the keyboard player had a big Mackie stereo setup and we ran the mics through his mixer to "help me make it through the night". On solo gigs on guitar, I use tracks on a laptop, carry two iPods loaded with tracks, and have tracks on CDs with a portable player stuffed in a travel bag. Must be prepared for the unexpected.