When practicing at home, always keep it fun and simple. Save the challenging stuff for a...
Many people (and all dogs) like that K9 Nose Work is an activity and sport where the dog is always rewarded for finding the source, whether it be self-rewarding on hidden food or a toy at the beginning stages, or handler-delivered reward for a correct find of a hidden odor at the highest level of competition.
Since a great deal of search and scent work for the dog is an expression of hunting instincts, it's important to learn what motivates your dog to hunt. Choosing the highest value reward for your dog in the beginning of your training will pay off down the road when the challenges increase.
The easiest way to tell if you have a toy dog or a food dog is to lay down both reward types side by side and see which one gets chosen first. Most dogs have a clear favorite, but if your dog likes both equally, just pick what will be easiest for you to handle and deliver to your dog as he progresses from searching for the reward only to searching for a target odor only.
Once you've discovered what reward type is most motivating to your dog, it's important to stick with it, especially in the beginning stages when the dog is self-rewarding and building his foundational skills for the activity and sport. If you notice a decrease in your dog's motivation to search, and have reason to believe the reward has lost value for your dog (rather than some other cause for lack of motivation, such as the searches becoming too difficult too fast), then a new reward can be introduced, but the process must begin again so your dog associates this new reward with all the foundational skills of the activity.
If you're having trouble choosing a reward, start by having your dog audition every toy and treat you own to see if something grabs his attention. If you still can't find that perfect motivator for your dog, attend a workshop or join a class and get some help from the K9 Nose Work pros!