When I ran pneumatics, undersized tubes always worked best for me when I'd have a flat. When using 700x28mm tires I would use 18x23mm tubes as my 'carry on' tubes as I could fit 2 of them in my seat bag. Tubes vary in size(as do tires) a great deal, so one brand's 28-32mm may be a great deal larger than another brand. Long stem presta's are what I would get because they would fit any rim in my group of bikes. Then when I got home I'd patch the punctured tube, replace the smaller one with it and deflate the smaller one and put it back in the seat bag. It was a bit of a process, but better to struggle a little bit at home than get a 'pinch flat' on a rainy day and have to do the whole 'road replacement' routine twice. Get a Topeak Road Morph w/guage for your pump. 30.00 w/no shipping from
http://www.bikeisland.com. Best deal on the best frame pump on the market. I'm not a shill, just believe in the integrity of the product and the vendor.
You wont find ANY presta tubes at Wal-Mart, K-Mart, Target, etc. as they only stock Schraeder tubes.
BTW, I've gone over to Nu-Teck airless on all of my bikes now. Just got a new commuter(Motobecane fantom/cx cyclocross) from bikesdirect.com and am running the stock 30mm pneumatics at present on it(w/2 18-23mm, long stem prestas in my seat bag
), but the 700x28mm 130 psi airless Touring tires are on the way.