Next to any temple, you’ll find small florists who specialize in garlands and other flowers for offerings and ceremonial uses (see some examples in my earlier “Car Puja” post). You can buy flowers for religious purposes or just to take home.
I am a fan of the simple white strings of jasmine. You buy them by the “hand” (a new and rather subjective unit of measure to me; it means the seller’s hand and not my super-sized American hand). They have been costing around 10, 15, or 20 rupees a hand <$0.40), depending on weather (cheaper after a thunder storm) and day (apparently they can be significantly more expensive on religious holidays).
I've seen ladies drape several hands of jasmine string in the hair at the base of a ponytail or top of a braid. I rode an elevator with someone who did this and she smelled so terrific! (I'm told this hair ornamentation is a rather old fashion style and kids these days don't want to sport the look. Such a shame.)
C coils then up around the Ganesh on the dashboard of the car (I guess it is an offering to Ganesh AND an air fresher!). Much better than the pine trees hanging from rear view mirrors of NYC taxis!