i use GarageBand more often than not for just this purpose.
There are quite a few DAWs for iOS out now and many of them are pretty full featured, but Garageband always works well for me and its easy to get a scratch drum track real quick.
I usually use my Apogee Jam because it kecks butt, but even the Griffin guitar connect cable works well for bass tracks. Not so much for guitar with amp sims on it though, too noisy.
Try it, you'll like it. Is fun!