Just got back from camping with the Scouts in cheapo 2/3-season tents. Went down to 5 degrees.

For car camping...bring a second bag. Can't hurt to have it. You can always put it under you. Having good ground insulation is key.

Change ALL of the clothes that you will be wearing to bed. Everying - top, bottom, socks, hat, gloves... This helps alot.

Next day, weather permitting, open up your tent and hang your open sleeping bag on a line to remove the night's moisture.