djb

as someone who commutes often with up to 20lbs in small rear panniers, one thing to think about is that just about any reasonable, cheap rear rack will easily and safely carry 20lbs of stuff, so a rack that costs 25 bucks and some rear panniers that are not expensive will get you an easy system that should hold the amount you are thinking of. Having a handlebar bag is always nice too, but my point is that for trying out bike travelling, you can do the rear rack and pannier route for not too much money.
The forementioned very light Arkel Dry-Lite panniers are a good option, and if you find you dont like bike touring that much, you can always sell panniers afterwards fairly easily and not lose that much money if they are in good shape. The main issue for you is heel clearance, so as Doug's photos show, smaller panniers will be better considering your road bike, and yes, those axiom rear racks do set the rack back more than regular racks, and work well. I put a streamliner on my wifes bike and the setback is a good couple of inches farther back than a traditional rack.

nun

Agreed. I started touring by strapping plastic bags onto a rear rack with bungie cords. If the OP has a rear rack already and some camping gear the Dry-lite route or simply stratping a few compressions sacks to the rack will work just fine.

nun

There is certainly a volume and weight threshold where racks and panniers are required, but I prefer the handling of a bike that uses a traditional saddlebag because the weight is kept close the center of mass of the bike/rider. Putting 4x 15lbs of panniers at the corners of the bike makes the bike more stable and sluggish and that's something I want to avoid. Putting stuff low down and far from the center of mass produces a big moment that is particularly uncomfortable for me at low speeds and when climbing. So tucking 15lbs up under the saddle is a way to minimize the changes in handling of my bike. I find that I can climb out of the saddle comfortably and I feel safer on descents.

shafter

I don't have a rack yet, which is why I am comparing them. Seat post vs Traditional vs Saddle bag for carrying a 20lb small pack?

nun

As you have lightweight camping experience you probably won't make the mistake of carrying too much stuff that most people new to touring and camping do. However, bikepacking and traditional saddlebags can be expensive and take some experience to set up correctly. So I'd advise a light weight rear rack, a set of Arkel Drylites and a handlebar bag.