Praise and Play
What's the one thing you always have with you, when you're out with your dog?
While treats may be rewarding to your dog, if you create tremendous value in giving your dog praise -- nothing will be better!
Praise can be a physical touch or a proud "good girl". Your dog must understand that you are pleased.
One very easy way to start priming the verbal "good" without a lot of excitement is randomly, and many times throughout the day catch them doing something right, say the word "good" and give your dog a treat with very little fanfare. The word will take on much greater meaning in time, even when no treat is present.
When you're training in public places where manners matter -
That "good" marker will have more meaning! Since you won't want to overly enthusiastic and cause your dog to get too excited and offer a bad behavior like jumping or breaking a down stay.
But if you are out training in the field with some room to let go, once you give the release queue and especially at the end of training, play actively with your dog, pet him love on him and verbally let him know how awesome he is.
You should be the ultimate reward for a job well done.
Having a few "jackpots" of rewards and the celebration with when you're training and practicing will help you achieve good behavior even when you can't bring out the cheerleaders and pom poms :-)