I've seen a lot of budgies hallowing out light wood so I guess getting a block and drill small holes and poke in nuts etc would be terrific for budgies to dig out, I use heavier wood for my amazon doing that. And I saw them selling blocks of light wood shaped into a bamboo shape with a hole started in it that was basically designed for budgies to dig out a nest from
For my budgie, I found a small "cage" into which I stuff paper, small ring toys, natural millet sprigs and so on. Wiki enjoys working those things out. Small vine balls can be used the same way.