First of all, I am not a budgie expert yet. What I do might not be the most recommended.
I use two different seeds mix.
As you can see in this thread, there are 4 food cups in the cage. I use the upper left one for water, and the two cups at the bottom for food.
In one of the two cups, I often uses Dr. Harvey's Our Best Parakeet Food. On the label it says: 11 seeds, 9 nuts, 9 vegetables, and 5 fruits. I have to point it out that my budgies ignore most of the dried fruit in there.
In the other cup at the bottom, I use my own mixture:
40% millet,
10% canary seeds,
10% hulled oat,
10% sesame seeds,
10% cracked corn,
20% some mixture of random veggie seeds I bought online.
For the cuttlebone, you can find them here. Do not forget a cuttlebone holder.