In The Bark magazine, Patricia McConnell has an article called "Rewards Redux" in which she discusses this very thing. I enjoyed the article when I read it, and in the online dog circles I follow, it keeps cropping up as more people discover it.
I've discussed this a little bit, in the Clicker Crossover: Loose Leash post. On walks, if I run out of treats but in other instances just to switch things up, I get Elka's play drive revved up. I have a variety of rope toys that I carry, and once she's stayed in the proper loose leash "bubble" for a proscribed amount of time, we have a round of tug, and then I let her shake the toy around for awhile, and maybe even carry it for a block.
Elka is not typically a high-drive dog, and her work ethic, well, needs working on. But she gets as attentive and drive-y as you'd ever like to see a dog when one of those toys comes out and she realizes that's how it's going to go. Elka is also already very food motivated, but that doesn't mean any treat will do. The value of the treat depends on the situation; in the kitchen, if we're doing "sit" and "down" and "stay" while I'm also cooking, green beans or carrots are just fine. If we're on the sidewalk, doing automatic sits and loose leash walking, it had better be hot dogs, or chicken, or pepperoni. Otherwise, she'll still take what I give her, and then just drop it on the sidewalk and turn her attention elsewhere.
Likewise, if we're at home and there are people over, even Gumby doesn't do it sometimes. Sometimes, you just have to give her the CocaCola box. Elka was so happy to have it in the first place, she paraded around the room a bit and wanted to share it with each person, but once that circuit was completed, she happily pulled it apart, dropping each piece on the floor. And then she curled up and went to sleep, apparently satisfied with a job well done.