Having a budgie can be so much fun! They can eat such a wide variety of foods so have fun with it and try out new things to help find out what they really enjoy!
Seeds, grated carrot, spinach, broccoli, corn and capsicum are all recommended when chopped or shredded but always just give a little of anything new to see how it goes.
Fruit is a great treat, you can try apple, banana, pear and berries.
Remember though, these are just occasional treats. They can also have cooked and cooled brown rice or quinoa.
Petbarn has a great variety of seeds etc but you could also try coles and Woolworths as they have a pet food section and also have the fruit and veg!
Good luck

Further to what the pther replies have proposed:
Fresh veg that budgees can eat – carrot, corn, capsicum, cucumber, brocoli or cooked (not hot) sweet potato.
Fresh fruit is great but does need seeds and pits removed.
Boiled eggs (mashed)
Cooked (not hot) brown rice and quinoa

Hope that helps!

Budgie seed mix. Millet. Fresh fruit. Dried fruit. Cuttlefish to keep their beak trim

Millet! You can buy them on small branch type things. My budgie loves it