Actually the president has more power than many think in this regard, without permission of congress the president can:
1) Return troops from abroad - cutting expensive foriegn deployments
2) Stop foreign aid to countries where it hasn't been mandated by law - Which is most if not all of it.
3) Stop unmandated entitlement expenditures - which currently unfortunately many of which are mandated by law but not all of them.
4) Propose bills in either house of congress - to pass of course these would need to be Congressionally voted on and approved but a president (with veto power and citizens favor) has a lot of pull.
5) Can veto any bill that comes across his desk, such as increased taxes, increased expenses, etc.
Basically it means he can stop things but he can't really start things right? If the congress refuses a bill that would put America well on track to reducing debt and boosting the economy, but severely impact the congressmen's interest, it's just not going to go through. If the congress keeps pushing bills to improve their own personal positions, all he can do is block and block isn't it? And IIRC, his veto power only means they need to get a higher vote percentage to push it through regardless of his objections isn't it?