there's nothing that says you can't use cut pieces from an old tube as opposed to purchased patches... after all, it's the rubber cement which does the holdin...
just need to make sure you clean the piece, from talc and other crappage, and rough up a bit as one would the actual tube to be repaired - never without a patch...

Multiple other uses of old tubes
long section, 'split' - makes great pre-wrap for bars before putting on the handlebar tape - gives some cush and also adds a little circumference - so more comfortable, without being clunky big...
quickie elastic wrap to hold ungainly stuff together - like assorted loose handlebars hanging around the shop - loose hockey sticks, ski poles, etc.
short 2" length cut section still a 'tube' - placed over frame pump head (if no cover or closure) keeps road dirt out of the head, especially on a wet ride.
cut to length section (MTB tube) makes nice sleeve for a small emergency tool so it doesn't scratch my reading glasses in the seatpack - same kind of tube section, just longer is a good sleeve for my small reading glasses in seat pack.
a length which is 'split' - used to wrap bike hanger hooks in garage, after the cheepie rubber coating splits - so the wheel doesn't get dinged when bike is hung...
...list goes on...