Whenever you venture outdoors -- whether you're bicycle touring, overnight camping or even just day-hiking --
consider carrying with you an inexpensive (usually $5-$10, at most),
extremely lightweight and very compact (folds up to about hand/palm
"space blanket" or two. These can
be a literal lifesaver if suddenly unexpected inclement weather should
roll in upon while you're far afield.
Space blankets -- aka: "survival blankets" -- are essentially aluminumized/foil-type plastic. They were developed for the NASA space program.
We have four of them ourselves: two sets that are kept with our bicycle camping equipment, and the other two with our other regular camping stuff.
You can usually easily find space blankets at retail outdoors-type stores and at Wal-Mart or Target in their "sporting goods" areas. They can also be found in many outdoor equipment catalogs, such as CAMPMOR.
One codicil: Space blankets can be a little noisy if you move around a lot, due to the aluminized aspect. But, it is precisely that aluminization that gives them such a good insulation factor! So, if you tend to, er, "recreate" during the evening/night in your tent, you will literally be making your own "music"...and possibly "entertaining" others in nearby tents.
Consider adding a layer of thick foam rubber between your sleeping bag and the air mattress for added insulation. In colder weather, air mattresses will become cold-air sinks; and, since they are essentially lying directly on the ground (with only the thin layer of tent-floor nylon between it and the ground) they will also remain fairly cold to lay upon in colder weather.
Even though you may not want to put out the initial outlay for better air mattresses -- like the Therma Rest self-inflating ones (which have a built-in insulating foam layer), do keep in mind that without the better, more efficient/effective equipment your camping experience may not be as pleasant or as comfortable as you might like. --- It's kind of like buying a cheap bicycle at a discount store -- with a cheap, non-anatomic/non-gelfoam, butt-pad saddle; and macho-low (TOO high/hard-to-pedal!) "low" gearing...you'll end up getting "turned off" to bicycling before you even had a chance to really experience what bicycling with proper/effective/efficient equipment is like!
See you ON the road!