Tubes are not expensive and it is possible, even with a good repair by an experienced cyclist, to have a leaker in a patch. But if I were budget conscious or didn't have easy access to new tubes I would patch it and not be overly concerned. I do prefer to have a new tube for repair on the road rather than a patched tube.

For what it's worth make sure you feel the inside (carefull, don't cut yourself) of the tire to make sure whatever flatted the first tube isn't stuck in the casing waiting in lay to puncture the second tube. Most often these items take many tire revolutions to work through the casing in to the tube and are often times lodged there. I run my finger tips along the inside looking for the thorn or broken bit of glass or tack or what have you. \

Don't forget to sweep your tires!