I put a set of Dunlop StrapLoks on each of my guitars. The straps are interchangeable, and I never have to worry about dropping an axe.

Another couple of items that haven't been mentioned yet:

[u]A tuner[/u]: nobody wants to wait around while you try to tune your guitar.

[u]An AC line checker[/u]: This thing is a plug with three small lights built into it. You plug it in to the AC outlet, and compare the lights to the chart on the tester. This thing can save your life by alerting you to wiring problems [u]before[/u] you get your gear hooked up!