I know how you feel, I had proper panic attacks at this time, heart racing, feelings of sheer terror, and pretty much paralysed my thinking. It does pass though. You are still in shock. You need to be very kind to yourself. So glad you have a friend coming, that is the best possible distraction.
Suggestions for your weekend:
Definitely get your nails done, and a haircut, make yourself feel pretty buy some new make up too - this sounds a bit woman magazine, but it helps, it really does.
Plan what you are eating for the entire weekend, only buy things you like (my ex hated fish, and I love it so on contact weekends I filled the fridge with smoked salmon, made an indulgent fish pie, went out for sushi etc). find something complicated to cook that will absorb you. Have a fabulous breakfast and buy lovely tea or cofee. Feel indulged.
Radio 4 and 4 extra, for listening to stuff that means you don't have to think while you are pottering around.
Box sets (netflix is best) depending on what you like, but (again) getting absorbed in a series that you can watch for a few hours at a time (I recommend The Walking Dead, Breaking Bad, the original The Killing (Forebrydelsen or something) or something lighter like The Midwives or even documentaries like Blue Planet)
Going to the cinema on your own is actually lovely if you feel you need to get out of the house. The first time I did it I felt a total loser, but once you're in no one notices or cares you are by yourself - this is a top Sunday afternoon tip, as Sunday afternoons are the worst times, I find)
Embrace social media, Facebook and twitter can be very good friends if you are feeling panicky or lonely, just say you are and people rally round and tell you you are awesome and share their experiences, it's distracting if nothing else.
Make your bedroom clean and tidy and sanctuary-like. Clean everything, change the sheets and get rid of any man nonsense, pop some flowers on the bedside table if you can.
None of these may feel right to you, and I can see they all look superficial, but you get the general (sorry, probably very waffly) idea. Don't feel guilty about spending time on you or just wasting time until you get your children back. It really is what other people do and it's ok.
Also post here for whatever you need to as well
There are quite a few of us willing you on.
As another 'be prepared' thingy, be prepared for your lovely children to be tired and cranky and a bit horrible when they get back, it doesn't mean anything other than they are confused and need you to be as stable as you can be. And you will because you sound like a fab mum.