As you build your foundation, it will be beneficial to your future training to teach your dog to happily work for whatever reward you happen to offer.
Treats work well for stationary behaviors, thoughtful mindsets, and when your dog needs to move carefully and with finesse.
Toys work well for acceleration behaviors, building drive, for overcoming physically challenging obstacles and to build bravado.
To teach your dog to value what you offer as a reward, start with play. Play with one thing, then when your dog is into the game, just drop that toy and go play with a different one – does dog leave the toy they “won” to play with you via a different toy? Do they bring the toy with them to try to play with both? Excellent - both are great responses.
Does the puppy run away with their toy? No problem, just play in a confined space or with a toy on a leash so that can't happen (or at least they can't get far). Now the game is to make your toy way more interesting and fun than the stupid old toy they just ran away with. Do not try to GET YOUR PUPPY TO PLAY - this is too much pressure on them and they are likely to back away from it. Instead, you play with the toy, make it leap, make it hide under your legs and then find it again, make it dance, jump on your head - channel your inner 3 year old and be delighted with your toy. If your puppy can't resist the urge to butt into the game - yeah! play for a short while and then put the puppy away - you will need the rest.
This stage is almost always more successful if you can get on the ground so you aren't looming over the puppy.
Here is another game: give the puppy some treats, then switch back to playing with a toy. Sometimes dogs who have learned to expect a treat are hesitant to engage in a game – use the rules of play to make it irresistible for your dog to join in.
Here is another one: hold a toy in each hand, tug with one toy, then let that hand go still – make the other toy come alive – can the dog let go and switch to the “live” toy?
It is hard to overstate how valuable this training is, but I will just say one last thing. I almost always get to meet future agility stars that train with me when they first come home (who can resist showing off their new baby) - and the puppies are happy to chase a little toy, stomp on it, sometimes grab it etc.. And then after 6 weeks of puppy class, almost all of them are reluctant to play. What happened? Nothing - other than that they have just spent 6 weeks learning how to work for treats and now that is what they expect to happen. It can be a big job rebuilding the value of play and toys - so keep that in balance right from the start and you are way ahead of the game.