That...varies. The right to a speedy trial can be waived. The right against enslavement cannot. You can consent to a warrantless or otherwise unreasonable search given adequate specificity, but outside of a condition for release from otherwise-constitutional more severe deprivation of liberty (e.g., parole from prison) I don't think it can be generally waived in advance, only searches specifically and immediately consented to when being executed. But I don't have any particular cases in mind, and that understanding could be wrong. But “constitutional rights can be waived” is definitely way to broad to be a good useful guide for resolving specific isssues.
There are limitations, of course. If you live off-post in private housing, your commander has no legal authority to inspect it. They can only go through your stuff if you live in government-owned housing.
That's not a waiver, that's a space warrantless searches are reasonable under the fourth amendment and Congress’ Art. I, Sec. 8 powers with regard to the military, etc. Otherwise, when we had conscription, conscripts, who do not freely consent, would have been immune.