I feel your pain. My husband has worked out of town Mon-Fri (he is home most weekends) for over a year now.
#1 If there is anything that only he does (bills, yard work, minor repairs, etc.) learn how to do it! If it's something you can't physically do, find out how he does it and decuss who you will get to do it if it needs done while he is out of town. You will both feel horribly helpless if something happens while he is stuck out of town and you are helpless there at home.
#2 Pack little notes or pictures for him to open/read while he is gone.
#3 Get one of the inexpensive digital photo key chains and fill it with pics of you and the kids. My hubby LOVES his. I think you can pick one up for under $20. You can take pics while he is gone and update it when he is home.
My son is 4 1/2. He has always been fine with my hubby being gone as long as my hubby tells him Sunday night that he will be sleeping at work that week. If he ever forgets to tell him (although it always happens) it's bad! He talks to him nightly as well.
In fact, it's gotten to where my DS is ready for my DH to leave if he's here more than a couple of days because he doesn't want to share me! lol
Good Luck with it! Just remember the separation is temporary and absence makes the heart grow fonder.