Anecdotally, one thing I observed as a lowly enlisted soldier is the need to panic spend money at the end of the fiscal year to make sure the budget next year wouldn't be smaller. Maybe we could start with practices like these.
Human nature is why we can't have nice things.
This is why I believe the scope of work should be clearly defined. Requests for funding submitted and approved with relation to that work. Then square up the taxes required based on what was spent, adjust up and down automatically.
Congress needs to vote to make that funding come out of the Rich (higher relative % of wealth the more taxed), to largely exempt anyone under an average (E.G. 10X poverty line is where taxes even START), and treat excess property as an Investment while exempting average ownership (E.G. a similar average for 'housing ownership' and 'transport ownership' value).
Using up money before it "goes away" and padding budgets should be expressly forbidden. Yes it's sometimes impossible to prove if it's happening, but you can say it's a standard and tell people to follow it, and catch blatant cases. Plenty of rules and standards are hard to prove.
"Waste" that is trimmed one year becomes the new bar "This can run at X".
Allocating additional resources requires far higher push than taking back something not spent.
Yet some years require more resources. What if there are more natural disasters? What if there's an economic downturn and more people need help? What if companies fail and expected taxes are not paid?
What if it's time to replace durable goods that have reached the end of their projected or useful life? (E.G. Some disgruntled person came to court with a shotgun and fired at all the computers; and oh BTW they're both broke and in jail so there's no cash to be had.)
You can see the very reluctance and assumptions in other posts in reply. They assume there are no audits, no oversight in the system. That the cursory pointer towards a larger process was the ENTIRE process which they then attack.