Best place to start is education. Cross reference student performance for the last 90 years: 45 years before and after the creation of the Dept of Education in 1979. Examine max/min/mean teacher pay adjusted for inflation for the several States, average student performance, minority success in schools, and administrative bloat in dollars spent per non-credentialed headcount (non-teachers).
Suspend execution of all DOE mandates and send all employees home, put a single bill in front of Congress for roll call votes to eliminate the agency and rescind 50% of its budget of about $270 billion annually in the form of structured income tax breaks, keep the other 50% to apply to the national annual deficit. The several States can adjust their own budgets accordingly and tax as they see fit to replace what they might have lost through elimination of Federal budget reallocation/redistribution. I'd be shocked if a quarter of DOE funds actually made it back to school campuses.
Rinse and repeat with other departments. For BLM, begin a process of releasing 10% of Federal lands back to the western States they reside in, and cutting staff accordingly. They're only a $2 billion operation, but the land holdings are egregious and an insult to the integrity of the several western States and their parity with their eastern peers.
For DOD, some sort of budgetary oversight has to happen even with the classified stuff. A variation on the GAO with the authority to audit and expose/cull what is wasteful.
Social Security? Kill it. With fire. Pro-rate existing "benefits" for those that paid in so far, cut what you're taking out of everyone's paycheck in half right now. Pay the liabilities of those currently on SS with the halved amount for the next 20 years, then cut it in half again for another 20 years, then eliminate it. Boomers whining about being on a fixed income and they paid their fair share will be sent copies of Ida May Fuller's SS contribution documents and benefits statements, and asked to reconcile them. Then asked why they didn't fix it 50 years ago.