Hmm, probably going to be tricky with an LX3. You can get decent shots of the planes on the ground but for the air display you'll most likely only get decent shots which feature the planes against some kind of interesting background, as opposed to close ups, for which you would need a camera (preferably DSLR) with a fairly long telephoto (ideally at least 400mm equivalent).
I would be tempted to shoot JPEG + Raw or else use a sports scene mode. Shutter speeds of 1/500 should be adequate to stop the planes but take some test shots - it depends on how far away they are and the direction and plane of flight - sometimes you need a faster shutter speed than that. Bear in mind that you need a slower shutter speed with prop planes if you want a shot where the prop is a bit blurred - try 1/250 and experiment with speeds around that.
Watch out for under-exposure - any shots with lots of bright sky in will tend to fool a camera's meter into under-exposing, so most airshow shooters dial in exposure compensation - experiment with +1, +1.5, etc until you see what works for you in the weather conditions you have.
I guess the thing to do is to make the most of the LX3's wide angle, since you don't have much of a telephoto - so lots of pictures of the planes on the ground, getting in nice and close to the wings, nosecones, as well as pictures of detail, such as interesting markings. Maybe also some nice portraits of flight crew if they are around and willing to pose. Also try some different angles, such as really low down with max wide angle.
For the air show, again, you could use the wide angle if you can find some interesting foreground to include, such as control tower. Also don't forget photos of people watching the air show - can be interesting and fun.
Have fun and I hope the weather holds !
