Changi has the spas for the massages , so you can waste an hour there. You can waste several hours in the outside cacti beer garden, if you have the budget, or even just pop into Gheyland (10m away) for local eating house food and tiger beer ($4 for the food, $6 for a big bottle of beer) if you have just a couple of hours to kill (or, it is Gheyland, so you can also get a "massage" there too ;-) )

btw, Changi has complementary luggage storage services too. Just visit the "left baggage" counters and they do it all, for free. There is also a payable service, International Pte Ltd, in T1 and T2 (maybe T3 as well) for around $3 per 24 hours.

Also, like in all airports, just walk out the door to the nearest airport hotel, and leave the bags there, The baggage people never ever check if you have a current reservation at the hotel, and the service will also be free (with tips to be paid in America).
Hopped in the car and torpe'ed to the shack
Of Shaheed, "We gotta go back" when he said
"Why?" I said, "We gotta go
'Cause I left my wallet in El Segundo"