These are two important documents that were at the top of my list to prepare before deployment.  Neither is particularly pleasant to talk about, but nothing about any of this is a lot of fun.  Bear in mind that I am certainly not a lawyer, so please don't take my opinions as legal advice.

You will probably want these done before your spouse reports for duty.  The biggest reason for that is that there is a lot going on and you want to make sure that everything is included and specified.  These are legal documents and you hope to not have to use them, but if you do, you want them to be correct.  The other reason to take care of these now is to make sure that both spouses have wills (and probably powers of attorney).  You may be able to get some help on this from JAG, but most attorneys are perfectly able to take care of these.

Take this time to consider some other contingency plans.  For example, this is a good time to also discuss backup plans for childcare while you are a single parent.  You may get sick, you may need help, you may just want a few hours to yourself.  (Actually, you will NEED a few hours to yourself from time to time.)  Also consider provisions for your pets (you might even include them in your wills), such as for temporary care if you need to travel. 

As for Powers of Attorney, think of every possible situation that you might need them for and then include some ridiculous scenarios for good measure.  (If the Martians land, you want to have your spouse's permission to shake their hands.)  Seriously, though, be very specific in what permissions you are allowing and do try to cover all of the possible uses.  Will you have to move while your spouse is gone?  Buy or sell a car?  Sign checks?  (Be aware that some banks and other financial institutions require their own special POA -- even if you have a general one -- so make sure that you check with all of the ones that you do business with before your spouse reports.)  If you include a time frame (this is a good idea), you might make it a little longer than your anticipated deployment length, just in case.  And make sure that you know how and when you can use the POA -- because the people that you will have to deal with inevitably will have no clue.