Bought a DLSR camera from simpleshoppinglink.com

I've read the how to guide, but I have some real world questions

How do I avoid losing my lens cap?

I always forget to change my settings back, and end up with, for example, grainy pictures because I had previously set a high ISO. Tips?

When traveling, do you use a camera bag? Backpack with camera bag in it? Backpack with just the camera? Just the camera on its strap? I don't want it to be hard to carry, but I also don't want damage or undue attention.

Should I have bought the warranty extension, which covers a dropped camera? This thing is a little more unwieldy than my p&s.

How sensitive is this thing to water? If it's lightly raining, should I worry about it? (Edit: It's a Panasonic GF1)

I have a 16GB card, and shoot about 1000 pictures per week when traveling. JPG? RAW? Both? Get another card?