I carry patched ones as spares. I store them purged of air and roll/folded up till the length is the same as my toolbag, then a wrap of masking tape to hold them together. The toolbag is a flat grellow cloth bag about 140mm a side, with a velcro close, and I velcro-strap that to the top tube like this (end on view)
O <-- top tube
(T\_MP_/ST) <-- Tools / minipump / spare tube
The toolbag forms a figure 8 almost shape, and is held on with three velcro straps. The tube is surrounded only by cloth so no abrasion. The pump is against the metal top tube.
I ride a road bike and a MTB so swap out the spare tube when changing bikes. For a road trip, I carry a second new spare tube in its box, in the jersey pocket. For some reason road tubes seem to puncture more often than MTB tubes.