One bag inside the other works well, especially if one is larger - like a mummy winter bag inside a rectangular lighter bag. You want to try to maintain the loft. Sometimes I put a wool or fleece blanket inside the bag for that reason. But, getting some good insulation under you is a must.

When I said to change clothes, I usually just put on a single base layer of poly tops and bottoms (never cotton), some wool socks and a new hat. I have a mid layer nearby if needed. These all become my next day wear, then get changed again at bed time.

Again, the great thing about car camping is that you can take more stuff than you need. I usually have a couple extra bags and blankets for any scouts who might need them.

Oh, if you want, get some hand and feet warmers. I know some troops that hand them out like candy. We don't but they are nice to have if really needed. You can also put one in a sock and stick it down the end of your sleeping bag.

Have fun!