• How to keep the camera in continuous shooting mode during the flight?

The continuous shooting mode is different for each camera, and not all cameras have it. Check the camera selection page.

Some cameras can be programmatically, such as Canons using the Canon Hack Development Kit (CHDK). Some Canons can also also be triggered by infrared remote control codes, useful for stereo or near infrared camera pairs, along with Stereo DataMaker. Cris Benton and others use motors to trigger cameras that can't be programmed.

Taking lots of photos is generally easier than controlling when a photo is taken. Once you find a camera with continuous shot, test the battery to see how long it will shoot. Put in a memory card with 4gb+. Consider getting a second battery.

Super Simple- Holding Down the Shutter

This is for use with the PET Bottle Rig

Instead of using a balled up piece of tape, a pebble, or some other thing to hold down my camera's shutter, I've gone to using a knot. This makes it easy to hold in place, and makes setting it easier. I prefer a rubber band, but tape also holds it down. tape may be more useful for bulging, non rectangular cameras.

My Canon SD1000 needs the rubber band tripled up to hold it in place:

source: http://publiclaboratory.org/notes/mathew/1-29-2012/using-knot-trigger-cameras