I would just feed alfalfa hay and alfalfa pellets until he reaches 6 months old (introduce veg at 4 mo. as earlier posted).
You can buy storebought treats, but no yogurt drops or anything with seeds. Storebought treats are like junk food for rabbits, they aren’t good for them but I am still addicted to buying them… My bunnies usually get bits of fruit or carrot (a much healthier treat option) in the morning, and one storbought treat in the evening before bedtime. I usually buy treats from Petsmart (my rabbits love the tart biscuits, veggies biscuits, veggie sticks, and they go bannanas for the dried fruit medley. ha ha get it, nevermind…)
, or Supreme Crunchies.
If you live in the U.S or Canada, there’s a U.K brand called Boredom Breakers that you can buy off Amazon or Bobbys Bunny Boutique. They make really healthy rabbit treats and forages that my bunnies love, and can eat a little more of because they are so healthy.
I also like making my own treats sometimes by baking a mix of old fashioned oats, pellets, water, and fruit (apple+rasberry, or bannanna, or rasberry). I usually store them in the fridge or else they get moldy.