Currently “emergency powers” means free-for-all, shut down the press, imprison everyone, etc. To help avoid this situation, we should be explicit about which powers that differ from normal government, are helpful in each situation.
Natural disaster: here the exigency is making sure survivors are helped (manpower, some critical supplies and equipment) and critical supplies like fresh water are available. A secondary objective is trying to limit additional property damage or other crime due to the lack of manpower, which is being diverted to survivors. In this case, money is available since usually a natural disaster affects a small portion of the country. Therefore, price control per se is not indicated, rather buying at the market price and ensuring purchases can be made because goods are made available. For the manpower, a draft of responders, commensurate to the work to be performed, is indicated; but again because money is available, this can’t be free labor, the individuals drafted have to be compensated relative to their existing income, or the wage rate that accords to the task they are assigned, whichever is higher. As for movement restrictions, they only make sense to apply to the affected areas and would be lifted when manpower is more available and access to the area is easier.
Spread of highly contagious disease: the primary issue is ensuring adequate medical supplies and staff are available. To that end, a draft of qualified individuals, or bulk labor as needed, is required; but since the country has money, this has to be paid service of the higher of old job or new job/assignment wages. The secondary issue is preventing the spread by movement restrictions. If there is no way to tell who is infected until it’s too late, a general quarantine may be ordered. If there is a means to clear individuals via quarantine period or test, then these are allowable to require, prior to allowing movement/travel. If only a certain area currently is infected, then cordoning that area and enforcing quarantine there is acceptable; but for travel within and among non-affected or contained areas, no movement restriction is justified (otherwise you could have a long running imprisonment for trace infections). There may also be limited shortages depending on the scope of the infection, but again the country has money, so goods need to be paid for according to their cost to produce + normal profit + additional capital investment needed to increase production.
Total war (lesser war cannot be an emergency situation, this is a common pretext for imprisoning the citizens): manpower and goods both are in short supply. Additionally, the government has no money. In contrast to other situations, requisition of required manpower and goods may be on a (momentarily) uncompensated basis, to be paid down with debt service over time (since there is no money). In the most extreme case – that debt service has become absurd – theft and unpaid forced labor is acceptable (but you’re probably screwed at that point). There is one other issue that comes up: censorship, along with movement restrictions to prevent spying e.g. on harbors where ships leave port. The allowable scope is much less than you would think, even though an impact to operational availability could be deduced from a wide variety of reports. Here is the problem: say that the commander in chief is not conducting battle effectively, or is not coordinating production/ordering the correct items to be built. How would you correct these problems, which clearly have important battlefield implications? You would make the claim and then support it with evidence. This requires the report to be made, then a group of independent investigators/citizens have to look into it. That in turn compromises the information at some average rate. However, the benefit from correcting those issues far outweighs the operational impact of the leaking of the relevant information. Further, as voters will be called on over the course of such a war, a relevant summary has to be made available to them, almost ensuring the enemy will receive the reports. So, only information that doesn’t indicate a problem, or is not needed to diagnose an issue or generally to understand the high level strategy, can be censored. Likewise, movement around non-sensitive areas, or communications about non-sensitive topics, cannot be restricted (other than by manpower needs e.g. the draft, or limitations e.g. of gasoline).
A tricky question for the total war case comes up with encryption and the question of whether communications can be monitored. In an emergency, can encryption be removed? In 2020, there are too many encrypted media and too many devices to update, that if in fact such encryption were infeasible to break in bulk, that in an emergency situation you actually could recall all of them, because the manpower required to make all those changes in the short amount of time is infeasible to requisition vs. alternatives. You would have to implement a far-reaching economic program to backdoor/compromise all encryption well in advance of the emergency, because hard cutting off all encrypted traffic means breaking most every networked system, sabotaging the economy (you can do it but the benefit is outweighed by the hindrance to the war effort). Even if you do this, the wide variety e.g. of wireless communications, means the enemy probably still can communicate coded messages if they have a backhaul somewhere that they can move the data back out to their analysts. So the answer is, not really – you could lay down that infrastructure, but it would cost you a ton of money, weaken your overall defenses because of the compromised encryption, and the enemy probably can get their messages out anyway.