When filing tax a return, a list of programs that need funding would be given. Tax payers with be shown in real time how much funding the programs need, current funding levels, and blanks to choose how many dollars to fund these programs with. A ranking system of what the people think is important should also be provided. Each tax return gets 1 vote per dependent and 1 vote for single filer, 2 votes for joint.
Imagine a website like go fund me with real time updates and progress bars as people submit their returns. Over funding is allowed - space exploration for example may get a nice budget expansion.
The taxes would be optional. Tariffs would fill the gap between program needs and taxes collected, these funds would be divided out based on tax payer votes.
“Put Your Money Where Your Mouth Is Act” has a nice ring to it.